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- 20 Aug, 2021 5 commits
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Will Deacon authored
In preparation for saving and restoring the user-requested CPU affinity mask of a task, add a new cpumask_t pointer to 'struct task_struct'. If the pointer is non-NULL, then the mask is copied across fork() and freed on task exit. Signed-off-by:
Will Deacon <will@kernel.org> Signed-off-by:
Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by:
Valentin Schneider <Valentin.Schneider@arm.com> Link: https://lore.kernel.org/r/20210730112443.23245-7-will@kernel.org
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Will Deacon authored
Reject explicit requests to change the affinity mask of a task via set_cpus_allowed_ptr() if the requested mask is not a subset of the mask returned by task_cpu_possible_mask(). This ensures that the 'cpus_mask' for a given task cannot contain CPUs which are incapable of executing it, except in cases where the affinity is forced. Signed-off-by:
Quentin Perret <qperret@google.com> Link: https://lore.kernel.org/r/20210730112443.23245-6-will@kernel.org
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Will Deacon authored
select_fallback_rq() only needs to recheck for an allowed CPU if the affinity mask of the task has changed since the last check. Return a 'bool' from cpuset_cpus_allowed_fallback() to indicate whether the affinity mask was updated, and use this to elide the allowed check when the mask has been left alone. No functional change. Suggested-by:
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Will Deacon authored
Asymmetric systems may not offer the same level of userspace ISA support across all CPUs, meaning that some applications cannot be executed by some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do not feature support for 32-bit applications on both clusters. On such a system, we must take care not to migrate a task to an unsupported CPU when forcefully moving tasks in select_fallback_rq() in response to a CPU hot-unplug operation. Introduce a task_cpu_possible_mask() hook which, given a task argument, allows an architecture to return a cpumask of CPUs that are capable of executing that task. The default implementation returns the cpu_possible_mask, since sane machines do not suffer from per-cpu ISA limitations that affect scheduling. The new mask is used when selecting the fallback runqueue as a last resort before forcing a migration to the first active CPU. Signed-off-by:
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Josh Don authored
This extends SCHED_IDLE to cgroups. Interface: cgroup/cpu.idle. 0: default behavior 1: SCHED_IDLE Extending SCHED_IDLE to cgroups means that we incorporate the existing aspects of SCHED_IDLE; a SCHED_IDLE cgroup will count all of its descendant threads towards the idle_h_nr_running count of all of its ancestor cgroups. Thus, sched_idle_rq() will work properly. Additionally, SCHED_IDLE cgroups are configured with minimum weight. There are two key differences between the per-task and per-cgroup SCHED_IDLE interface: - The cgroup interface allows tasks within a SCHED_IDLE hierarchy to maintain their relative weights. The entity that is "idle" is the cgroup, not the tasks themselves. - Since the idle entity is the cgroup, our SCHED_IDLE wakeup preemption decision is not made by comparing the current task with the woken task, but rather by comparing their matching sched_entity. A typical use-case for this is a user that creates an idle and a non-idle subtree. The non-idle subtree will dominate competition vs the idle subtree, but the idle subtree will still be high priority vs other users on the system. The latter is accomplished via comparing matching sched_entity in the waken preemption path (this could also be improved by making the sched_idle_rq() decision dependent on the perspective of a specific task). For now, we maintain the existing SCHED_IDLE semantics. Future patches may make improvements that extend how we treat SCHED_IDLE entities. The per-task_group idle field is an integer that currently only holds either a 0 or a 1. This is explicitly typed as an integer to allow for further extensions to this API. For example, a negative value may indicate a highly latency-sensitive cgroup that should be preferred for preemption/placement/etc. Signed-off-by:Josh Don <joshdon@google.com> Signed-off-by:
Vincent Guittot <vincent.guittot@linaro.org> Link: https://lore.kernel.org/r/20210730020019.1487127-2-joshdon@google.com
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- 10 Aug, 2021 1 commit
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Sebastian Andrzej Siewior authored
The functions get_online_cpus() and put_online_cpus() have been deprecated during the CPU hotplug rework. They map directly to cpus_read_lock() and cpus_read_unlock(). Replace deprecated CPU-hotplug functions with the official version. The behavior remains unchanged. Signed-off-by:
Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20210803141621.780504-33-bigeasy@linutronix.de
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- 06 Aug, 2021 2 commits
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Quentin Perret authored
SCHED_FLAG_KEEP_PARAMS can be passed to sched_setattr to specify that the call must not touch scheduling parameters (nice or priority). This is particularly handy for uclamp when used in conjunction with SCHED_FLAG_KEEP_POLICY as that allows to issue a syscall that only impacts uclamp values. However, sched_setattr always checks whether the priorities and nice values passed in sched_attr are valid first, even if those never get used down the line. This is useless at best since userspace can trivially bypass this check to set the uclamp values by specifying low priorities. However, it is cumbersome to do so as there is no single expression of this that skips both RT and CFS checks at once. As such, userspace needs to query the task policy first with e.g. sched_getattr and then set sched_attr.sched_priority accordingly. This is racy and slower than a single call. As the priority and nice checks are useless when SCHED_FLAG_KEEP_PARAMS is specified, simply inherit them in this case to match the policy inheritance of SCHED_FLAG_KEEP_POLICY. Reported-by:
Wei Wang <wvw@google.com> Signed-off-by:
Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by:
Qais Yousef <qais.yousef@arm.com> Link: https://lore.kernel.org/r/20210805102154.590709-3-qperret@google.com
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Quentin Perret authored
The UCLAMP_FLAG_IDLE flag is set on a runqueue when dequeueing the last uclamp active task (that is, when buckets.tasks reaches 0 for all buckets) to maintain the last uclamp.max and prevent blocked util from suddenly becoming visible. However, there is an asymmetry in how the flag is set and cleared which can lead to having the flag set whilst there are active tasks on the rq. Specifically, the flag is cleared in the uclamp_rq_inc() path, which is called at enqueue time, but set in uclamp_rq_dec_id() which is called both when dequeueing a task _and_ in the update_uclamp_active() path. As a result, when both uclamp_rq_{dec,ind}_id() are called from update_uclamp_active(), the flag ends up being set but not cleared, hence leaving the runqueue in a broken state. Fix this by clearing the flag in update_uclamp_active() as well. Fixes: e496187d ("sched/uclamp: Enforce last task's UCLAMP_MAX") Reported-by:Rick Yiu <rickyiu@google.com> Signed-off-by:
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- 04 Aug, 2021 2 commits
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Quentin Perret authored
SCHED_FLAG_SUGOV is supposed to be a kernel-only flag that userspace cannot interact with. However, sched_getattr() currently reports it in sched_flags if called on a sugov worker even though it is not actually defined in a UAPI header. To avoid this, make sure to clean-up the sched_flags field in sched_getattr() before returning to userspace. Signed-off-by:
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Wang Hui authored
activate_task/deactivate_task will change on_rq status, no need to do it again. Signed-off-by:
Wang Hui <john.wanghui@huawei.com> Signed-off-by:
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- 28 Jun, 2021 1 commit
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Yuan ZhaoXiong authored
On a 128 cores AMD machine, there are 8 cores in nohz_full mode, and the others are used for housekeeping. When many housekeeping cpus are in idle state, we can observe huge time burn in the loop for searching nearest busy housekeeper cpu by ftrace. 9) | get_nohz_timer_target() { 9) | housekeeping_test_cpu() { 9) 0.390 us | housekeeping_get_mask.part.1(); 9) 0.561 us | } 9) 0.090 us | __rcu_read_lock(); 9) 0.090 us | housekeeping_cpumask(); 9) 0.521 us | housekeeping_cpumask(); 9) 0.140 us | housekeeping_cpumask(); ... 9) 0.500 us | housekeeping_cpumask(); 9) | housekeeping_any_cpu() { 9) 0.090 us | housekeeping_get_mask.part.1(); 9) 0.100 us | sched_numa_find_closest(); 9) 0.491 us | } 9) 0.100 us | __rcu_read_unlock(); 9) + 76.163 us | } for_each_cpu_and() is a micro function, so in get_nohz_timer_target() function the for_each_cpu_and(i, sched_domain_span(sd), housekeeping_cpumask(HK_FLAG_TIMER)) equals to below: for (i = -1; i = cpumask_next_and(i, sched_domain_span(sd), housekeeping_cpumask(HK_FLAG_TIMER)), i < nr_cpu_ids;) That will cause that housekeeping_cpumask() will be invoked many times. The housekeeping_cpumask() function returns a const value, so it is unnecessary to invoke it every time. This patch can minimize the worst searching time from ~76us to ~16us in my testing. Similarly, the find_new_ilb() function has the same problem. Co-developed-by:Li RongQing <lirongqing@baidu.com> Signed-off-by:
Yuan ZhaoXiong <yuanzhaoxiong@baidu.com> Signed-off-by:
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- 24 Jun, 2021 1 commit
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Huaixin Chang authored
The CFS bandwidth controller limits CPU requests of a task group to quota during each period. However, parallel workloads might be bursty so that they get throttled even when their average utilization is under quota. And they are latency sensitive at the same time so that throttling them is undesired. We borrow time now against our future underrun, at the cost of increased interference against the other system users. All nicely bounded. Traditional (UP-EDF) bandwidth control is something like: (U = \Sum u_i) <= 1 This guaranteeds both that every deadline is met and that the system is stable. After all, if U were > 1, then for every second of walltime, we'd have to run more than a second of program time, and obviously miss our deadline, but the next deadline will be further out still, there is never time to catch up, unbounded fail. This work observes that a workload doesn't always executes the full quota; this enables one to describe u_i as a statistical distribution. For example, have u_i = {x,e}_i, where x is the p(95) and x+e p(100) (the traditional WCET). This effectively allows u to be smaller, increasing the efficiency (we can pack more tasks in the system), but at the cost of missing deadlines when all the odds line up. However, it does maintain stability, since every overrun must be paired with an underrun as long as our x is above the average. That is, suppose we have 2 tasks, both specify a p(95) value, then we have a p(95)*p(95) = 90.25% chance both tasks are within their quota and everything is good. At the same time we have a p(5)p(5) = 0.25% chance both tasks will exceed their quota at the same time (guaranteed deadline fail). Somewhere in between there's a threshold where one exceeds and the other doesn't underrun enough to compensate; this depends on the specific CDFs. At the same time, we can say that the worst case deadline miss, will be \Sum e_i; that is, there is a bounded tardiness (under the assumption that x+e is indeed WCET). The benefit of burst is seen when testing with schbench. Default value of kernel.sched_cfs_bandwidth_slice_us(5ms) and CONFIG_HZ(1000) is used. mkdir /sys/fs/cgroup/cpu/test echo $$ > /sys/fs/cgroup/cpu/test/cgroup.procs echo 100000 > /sys/fs/cgroup/cpu/test/cpu.cfs_quota_us echo 100000 > /sys/fs/cgroup/cpu/test/cpu.cfs_burst_us ./schbench -m 1 -t 3 -r 20 -c 80000 -R 10 The average CPU usage is at 80%. I run this for 10 times, and got long tail latency for 6 times and got throttled for 8 times. Tail latencies are shown below, and it wasn't the worst case. Latency percentiles (usec) 50.0000th: 19872 75.0000th: 21344 90.0000th: 22176 95.0000th: 22496 *99.0000th: 22752 99.5000th: 22752 99.9000th: 22752 min=0, max=22727 rps: 9.90 p95 (usec) 22496 p99 (usec) 22752 p95/cputime 28.12% p99/cputime 28.44% The interferenece when using burst is valued by the possibilities for missing the deadline and the average WCET. Test results showed that when there many cgroups or CPU is under utilized, the interference is limited. More details are shown in: https://lore.kernel.org/lkml/5371BD36-55AE-4F71-B9D7-B86DC32E3D2B@linux.alibaba.com/Co-developed-by:Shanpei Chen <shanpeic@linux.alibaba.com> Signed-off-by:
Tianchen Ding <dtcccc@linux.alibaba.com> Signed-off-by:
Huaixin Chang <changhuaixin@linux.alibaba.com> Signed-off-by:
Ben Segall <bsegall@google.com> Acked-by:
Tejun Heo <tj@kernel.org> Link: https://lore.kernel.org/r/20210621092800.23714-2-changhuaixin@linux.alibaba.com
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- 22 Jun, 2021 1 commit
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Qais Yousef authored
Now cpu.uclamp.min acts as a protection, we need to make sure that the uclamp request of the task is within the allowed range of the cgroup, that is it is clamp()'ed correctly by tg->uclamp[UCLAMP_MIN] and tg->uclamp[UCLAMP_MAX]. As reported by Xuewen [1] we can have some corner cases where there's inversion between uclamp requested by task (p) and the uclamp values of the taskgroup it's attached to (tg). Following table demonstrates 2 corner cases: | p | tg | effective -----------+-----+------+----------- CASE 1 -----------+-----+------+----------- uclamp_min | 60% | 0% | 60% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- CASE 2 -----------+-----+------+----------- uclamp_min | 0% | 30% | 30% -----------+-----+------+----------- uclamp_max | 20% | 50% | 20% -----------+-----+------+----------- With this fix we get: | p | tg | effective -----------+-----+------+----------- CASE 1 -----------+-----+------+----------- uclamp_min | 60% | 0% | 50% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- CASE 2 -----------+-----+------+----------- uclamp_min | 0% | 30% | 30% -----------+-----+------+----------- uclamp_max | 20% | 50% | 30% -----------+-----+------+----------- Additionally uclamp_update_active_tasks() must now unconditionally update both UCLAMP_MIN/MAX because changing the tg's UCLAMP_MAX for instance could have an impact on the effective UCLAMP_MIN of the tasks. | p | tg | effective -----------+-----+------+----------- old -----------+-----+------+----------- uclamp_min | 60% | 0% | 50% -----------+-----+------+----------- uclamp_max | 80% | 50% | 50% -----------+-----+------+----------- *new* -----------+-----+------+----------- uclamp_min | 60% | 0% | *60%* -----------+-----+------+----------- uclamp_max | 80% |*70%* | *70%* -----------+-----+------+----------- [1] https://lore.kernel.org/lkml/CAB8ipk_a6VFNjiEnHRHkUMBKbA+qzPQvhtNjJ_YNzQhqV_o8Zw@mail.gmail.com/ Fixes: 0c18f2ec ("sched/uclamp: Fix wrong implementation of cpu.uclamp.min") Reported-by:
Xuewen Yan <xuewen.yan94@gmail.com> Signed-off-by:
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- 18 Jun, 2021 3 commits
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Peter Zijlstra authored
Change the type and name of task_struct::state. Drop the volatile and shrink it to an 'unsigned int'. Rename it in order to find all uses such that we can use READ_ONCE/WRITE_ONCE as appropriate. Signed-off-by:
Daniel Bristot de Oliveira <bristot@redhat.com> Acked-by:
Daniel Thompson <daniel.thompson@linaro.org> Link: https://lore.kernel.org/r/20210611082838.550736351@infradead.org
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Peter Zijlstra authored
Remove yet another few p->state accesses. Signed-off-by:
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Peter Zijlstra authored
Replace a bunch of 'p->state == TASK_RUNNING' with a new helper: task_is_running(p). Signed-off-by:
Davidlohr Bueso <dave@stgolabs.net> Acked-by:
Geert Uytterhoeven <geert@linux-m68k.org> Acked-by:
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- 17 Jun, 2021 1 commit
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Peter Zijlstra authored
This is a partial forward-port of Peter Ziljstra's work first posted at: https://lore.kernel.org/lkml/20180530142236.667774973@infradead.org/ Currently select_idle_cpu()'s proportional scheme uses the average idle time *for when we are idle*, that is temporally challenged. When a CPU is not at all idle, we'll happily continue using whatever value we did see when the CPU goes idle. To fix this, introduce a separate average idle and age it (the existing value still makes sense for things like new-idle balancing, which happens when we do go idle). The overall goal is to not spend more time scanning for idle CPUs than we're idle for. Otherwise we're inhibiting work. This means that we need to consider the cost over all the wake-ups between consecutive idle periods. To track this, the scan cost is subtracted from the estimated average idle time. The impact of this patch is related to workloads that have domains that are fully busy or overloaded. Without the patch, the scan depth may be too high because a CPU is not reaching idle. Due to the nature of the patch, this is a regression magnet. It potentially wins when domains are almost fully busy or overloaded -- at that point searches are likely to fail but idle is not being aged as CPUs are active so search depth is too large and useless. It will potentially show regressions when there are idle CPUs and a deep search is beneficial. This tbench result on a 2-socket broadwell machine partially illustates the problem 5.13.0-rc2 5.13.0-rc2 vanilla sched-avgidle-v1r5 Hmean 1 445.02 ( 0.00%) 451.36 * 1.42%* Hmean 2 830.69 ( 0.00%) 846.03 * 1.85%* Hmean 4 1350.80 ( 0.00%) 1505.56 * 11.46%* Hmean 8 2888.88 ( 0.00%) 2586.40 * -10.47%* Hmean 16 5248.18 ( 0.00%) 5305.26 * 1.09%* Hmean 32 8914.03 ( 0.00%) 9191.35 * 3.11%* Hmean 64 10663.10 ( 0.00%) 10192.65 * -4.41%* Hmean 128 18043.89 ( 0.00%) 18478.92 * 2.41%* Hmean 256 16530.89 ( 0.00%) 17637.16 * 6.69%* Hmean 320 16451.13 ( 0.00%) 17270.97 * 4.98%* Note that 8 was a regression point where a deeper search would have helped but it gains for high thread counts when searches are useless. Hackbench is a more extreme example although not perfect as the tasks idle rapidly hackbench-process-pipes 5.13.0-rc2 5.13.0-rc2 vanilla sched-avgidle-v1r5 Amean 1 0.3950 ( 0.00%) 0.3887 ( 1.60%) Amean 4 0.9450 ( 0.00%) 0.9677 ( -2.40%) Amean 7 1.4737 ( 0.00%) 1.4890 ( -1.04%) Amean 12 2.3507 ( 0.00%) 2.3360 * 0.62%* Amean 21 4.0807 ( 0.00%) 4.0993 * -0.46%* Amean 30 5.6820 ( 0.00%) 5.7510 * -1.21%* Amean 48 8.7913 ( 0.00%) 8.7383 ( 0.60%) Amean 79 14.3880 ( 0.00%) 13.9343 * 3.15%* Amean 110 21.2233 ( 0.00%) 19.4263 * 8.47%* Amean 141 28.2930 ( 0.00%) 25.1003 * 11.28%* Amean 172 34.7570 ( 0.00%) 30.7527 * 11.52%* Amean 203 41.0083 ( 0.00%) 36.4267 * 11.17%* Amean 234 47.7133 ( 0.00%) 42.0623 * 11.84%* Amean 265 53.0353 ( 0.00%) 47.7720 * 9.92%* Amean 296 60.0170 ( 0.00%) 53.4273 * 10.98%* Stddev 1 0.0052 ( 0.00%) 0.0025 ( 51.57%) Stddev 4 0.0357 ( 0.00%) 0.0370 ( -3.75%) Stddev 7 0.0190 ( 0.00%) 0.0298 ( -56.64%) Stddev 12 0.0064 ( 0.00%) 0.0095 ( -48.38%) Stddev 21 0.0065 ( 0.00%) 0.0097 ( -49.28%) Stddev 30 0.0185 ( 0.00%) 0.0295 ( -59.54%) Stddev 48 0.0559 ( 0.00%) 0.0168 ( 69.92%) Stddev 79 0.1559 ( 0.00%) 0.0278 ( 82.17%) Stddev 110 1.1728 ( 0.00%) 0.0532 ( 95.47%) Stddev 141 0.7867 ( 0.00%) 0.0968 ( 87.69%) Stddev 172 1.0255 ( 0.00%) 0.0420 ( 95.91%) Stddev 203 0.8106 ( 0.00%) 0.1384 ( 82.92%) Stddev 234 1.1949 ( 0.00%) 0.1328 ( 88.89%) Stddev 265 0.9231 ( 0.00%) 0.0820 ( 91.11%) Stddev 296 1.0456 ( 0.00%) 0.1327 ( 87.31%) Again, higher thread counts benefit and the standard deviation shows that results are also a lot more stable when the idle time is aged. The patch potentially matters when a socket was multiple LLCs as the maximum search depth is lower. However, some of the test results were suspiciously good (e.g. specjbb2005 gaining 50% on a Zen1 machine) and other results were not dramatically different to other mcahines. Given the nature of the patch, Peter's full series is not being forward ported as each part should stand on its own. Preferably they would be merged at different times to reduce the risk of false bisections. Signed-off-by:
Mel Gorman <mgorman@techsingularity.net> Signed-off-by:
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- 04 Jun, 2021 1 commit
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Eric Dumazet authored
Revert commit 4698f88c ("sched/debug: Fix 'schedstats=enable' cmdline option"). After commit 6041186a ("init: initialize jump labels before command line option parsing") we can rely on jump label infra being ready for use when setup_schedstats() is called. Signed-off-by:
Eric Dumazet <edumazet@google.com> Signed-off-by:
Kees Cook <keescook@chromium.org> Acked-by:
Josh Poimboeuf <jpoimboe@redhat.com> Link: https://lkml.kernel.org/r/20210602112108.1709635-1-eric.dumazet@gmail.com
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- 01 Jun, 2021 2 commits
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Valentin Schneider authored
Will reported that the 'XXX __migrate_task() can fail' in migration_cpu_stop() can happen, and it *is* sort of a big deal. Looking at it some more, one will note there is a glaring hole in the deferred CPU selection: (w/ CONFIG_CPUSET=n, so that the affinity mask passed via taskset doesn't get AND'd with cpu_online_mask) $ taskset -pc 0-2 $PID # offline CPUs 3-4 $ taskset -pc 3-5 $PID `\ $PID may stay on 0-2 due to the cpumask_any_distribute() picking an offline CPU and __migrate_task() refusing to do anything due to cpu_is_allowed(). set_cpus_allowed_ptr() goes to some length to pick a dest_cpu that matches the right constraints vs affinity and the online/active state of the CPUs. Reuse that instead of discarding it in the affine_move_task() case. Fixes: 6d337eab ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Reported-by: -
Peter Zijlstra authored
Extend 8fb12156 ("init: Pin init task to the boot CPU, initially") to cover the new PF_NO_SETAFFINITY requirement. While there, move wait_for_completion(&kthreadd_done) into kernel_init() to make it absolutely clear it is the very first thing done by the init thread. Fixes: 570a752b ("lib/smp_processor_id: Use is_percpu_thread() instead of nr_cpus_allowed") Signed-off-by:
Borislav Petkov <bp@alien8.de> Link: https://lkml.kernel.org/r/YLS4mbKUrA3Gnb4t@hirez.programming.kicks-ass.net
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- 19 May, 2021 3 commits
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Masahiro Yamada authored
fair_sched_class->next no longer exists since commit: a87e749e ("sched: Remove struct sched_class::next field"). Now the sched_class order is specified by the linker script. Rewrite the comment in a more generic way. Signed-off-by:
Masahiro Yamada <masahiroy@kernel.org> Signed-off-by:
Ingo Molnar <mingo@kernel.org> Link: https://lore.kernel.org/r/20210519063709.323162-1-masahiroy@kernel.org
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Qais Yousef authored
cpu_cgroup_css_online() calls cpu_util_update_eff() without holding the uclamp_mutex or rcu_read_lock() like other call sites, which is a mistake. The uclamp_mutex is required to protect against concurrent reads and writes that could update the cgroup hierarchy. The rcu_read_lock() is required to traverse the cgroup data structures in cpu_util_update_eff(). Surround the caller with the required locks and add some asserts to better document the dependency in cpu_util_update_eff(). Fixes: 7226017a ("sched/uclamp: Fix a bug in propagating uclamp value in new cgroups") Reported-by:
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Qais Yousef authored
cpu.uclamp.min is a protection as described in cgroup-v2 Resource Distribution Model Documentation/admin-guide/cgroup-v2.rst which means we try our best to preserve the minimum performance point of tasks in this group. See full description of cpu.uclamp.min in the cgroup-v2.rst. But the current implementation makes it a limit, which is not what was intended. For example: tg->cpu.uclamp.min = 20% p0->uclamp[UCLAMP_MIN] = 0 p1->uclamp[UCLAMP_MIN] = 50% Previous Behavior (limit): p0->effective_uclamp = 0 p1->effective_uclamp = 20% New Behavior (Protection): p0->effective_uclamp = 20% p1->effective_uclamp = 50% Which is inline with how protections should work. With this change the cgroup and per-task behaviors are the same, as expected. Additionally, we remove the confusing relationship between cgroup and !user_defined flag. We don't want for example RT tasks that are boosted by default to max to change their boost value when they attach to a cgroup. If a cgroup wants to limit the max performance point of tasks attached to it, then cpu.uclamp.max must be set accordingly. Or if they want to set different boost value based on cgroup, then sysctl_sched_util_clamp_min_rt_default must be used to NOT boost to max and set the right cpu.uclamp.min for each group to let the RT tasks obtain the desired boost value when attached to that group. As it stands the dependency on !user_defined flag adds an extra layer of complexity that is not required now cpu.uclamp.min behaves properly as a protection. The propagation model of effective cpu.uclamp.min in child cgroups as implemented by cpu_util_update_eff() is still correct. The parent protection sets an upper limit of what the child cgroups will effectively get. Fixes: 3eac870a (sched/uclamp: Use TG's clamps to restrict TASK's clamps) Signed-off-by:
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- 18 May, 2021 1 commit
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Valentin Schneider authored
For all intents and purposes, the idle task is a per-CPU kthread. It isn't created via the same route as other pcpu kthreads however, and as a result it is missing a few bells and whistles: it fails kthread_is_per_cpu() and it doesn't have PF_NO_SETAFFINITY set. Fix the former by giving the idle task a kthread struct along with the KTHREAD_IS_PER_CPU flag. This requires some extra iffery as init_idle() call be called more than once on the same idle task. Signed-off-by:
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- 12 May, 2021 16 commits
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Alexey Dobriyan authored
Runqueue ->nr_iowait counters are 32-bit anyway. Propagate 32-bitness into other code, but don't try too hard. Signed-off-by:
Alexey Dobriyan <adobriyan@gmail.com> Signed-off-by:
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Alexey Dobriyan authored
Creating 2**32 tasks to wait in D-state is impossible and wasteful. Return "unsigned int" and save on REX prefixes. Signed-off-by:
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Alexey Dobriyan authored
Creating 2**32 tasks is impossible due to futex pid limits and wasteful anyway. Nobody has done it. Bring nr_running() into 32-bit world to save on REX prefixes. Signed-off-by:
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Ingo Molnar authored
A few more snuck in. Also capitalize 'CPU' while at it. Signed-off-by: -
Valentin Schneider authored
As pointed out by commit de9b8f5d ("sched: Fix crash trying to dequeue/enqueue the idle thread") init_idle() can and will be invoked more than once on the same idle task. At boot time, it is invoked for the boot CPU thread by sched_init(). Then smp_init() creates the threads for all the secondary CPUs and invokes init_idle() on them. As the hotplug machinery brings the secondaries to life, it will issue calls to idle_thread_get(), which itself invokes init_idle() yet again. In this case it's invoked twice more per secondary: at _cpu_up(), and at bringup_cpu(). Given smp_init() already initializes the idle tasks for all *possible* CPUs, no further initialization should be required. Now, removing init_idle() from idle_thread_get() exposes some interesting expectations with regards to the idle task's preempt_count: the secondary startup always issues a preempt_disable(), requiring some reset of the preempt count to 0 between hot-unplug and hotplug, which is currently served by idle_thread_get() -> idle_init(). Given the idle task is supposed to have preemption disabled once and never see it re-enabled, it seems that what we actually want is to initialize its preempt_count to PREEMPT_DISABLED and leave it there. Do that, and remove init_idle() from idle_thread_get(). Secondary startups were patched via coccinelle: @begone@ @@ -preempt_disable(); ... cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); Signed-off-by:
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Peter Zijlstra authored
In order to not have to use pid_struct, create a new, smaller, structure to manage task cookies for core scheduling. Signed-off-by:
Don Hiatt <dhiatt@digitalocean.com> Tested-by:
Hongyu Ning <hongyu.ning@linux.intel.com> Tested-by:
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Peter Zijlstra authored
When a sibling is forced-idle to match the core-cookie; search for matching tasks to fill the core. rcu_read_unlock() can incur an infrequent deadlock in sched_core_balance(). Fix this by using the RCU-sched flavor instead. Signed-off-by:
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Joel Fernandes (Google) authored
During force-idle, we end up doing cross-cpu comparison of vruntimes during pick_next_task. If we simply compare (vruntime-min_vruntime) across CPUs, and if the CPUs only have 1 task each, we will always end up comparing 0 with 0 and pick just one of the tasks all the time. This starves the task that was not picked. To fix this, take a snapshot of the min_vruntime when entering force idle and use it for comparison. This min_vruntime snapshot will only be used for cross-CPU vruntime comparison, and nothing else. A note about the min_vruntime snapshot and force idling: During selection: When we're not fi, we need to update snapshot. when we're fi and we were not fi, we must update snapshot. When we're fi and we were already fi, we must not update snapshot. Which gives: fib fi update 0 0 1 0 1 1 1 0 1 1 1 0 Where: fi: force-idled now fib: force-idled before So the min_vruntime snapshot needs to be updated when: !(fib && fi). Also, the cfs_prio_less() function needs to be aware of whether the core is in force idle or not, since it will be use this information to know whether to advance a cfs_rq's min_vruntime_fi in the hierarchy. So pass this information along via pick_task() -> prio_less(). Suggested-by:
Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:
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Joel Fernandes (Google) authored
The rationale is as follows. In the core-wide pick logic, even if need_sync == false, we need to go look at other CPUs (non-local CPUs) to see if they could be running RT. Say the RQs in a particular core look like this: Let CFS1 and CFS2 be 2 tagged CFS tags. Let RT1 be an untagged RT task. rq0 rq1 CFS1 (tagged) RT1 (no tag) CFS2 (tagged) Say schedule() runs on rq0. Now, it will enter the above loop and pick_task(RT) will return NULL for 'p'. It will enter the above if() block and see that need_sync == false and will skip RT entirely. The end result of the selection will be (say prio(CFS1) > prio(CFS2)): rq0 rq1 CFS1 IDLE When it should have selected: rq0 rq1 IDLE RT Suggested-by:
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Vineeth Pillai authored
If there is only one long running local task and the sibling is forced idle, it might not get a chance to run until a schedule event happens on any cpu in the core. So we check for this condition during a tick to see if a sibling is starved and then give it a chance to schedule. Signed-off-by:
Vineeth Pillai <viremana@linux.microsoft.com> Signed-off-by:
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Peter Zijlstra authored
Instead of only selecting a local task, select a task for all SMT siblings for every reschedule on the core (irrespective which logical CPU does the reschedule). Signed-off-by:
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Peter Zijlstra authored
Introduce task_struct::core_cookie as an opaque identifier for core scheduling. When enabled; core scheduling will only allow matching task to be on the core; where idle matches everything. When task_struct::core_cookie is set (and core scheduling is enabled) these tasks are indexed in a second RB-tree, first on cookie value then on scheduling function, such that matching task selection always finds the most elegible match. NOTE: *shudder* at the overhead... NOTE: *sigh*, a 3rd copy of the scheduling function; the alternative is per class tracking of cookies and that just duplicates a lot of stuff for no raisin (the 2nd copy lives in the rt-mutex PI code). [Joel: folded fixes] Signed-off-by:
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Peter Zijlstra authored
Stuff the meat of sched_core_put() into a work such that we can use sched_core_put() from atomic context. Signed-off-by:
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Peter Zijlstra authored
rq_lockp() includes a static_branch(), which is asm-goto, which is asm volatile which defeats regular CSE. This means that: if (!static_branch(&foo)) return simple; if (static_branch(&foo) && cond) return complex; Doesn't fold and we get horrible code. Introduce __rq_lockp() without the static_branch() on. Signed-off-by:
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Peter Zijlstra authored
Introduce the basic infrastructure to have a core wide rq->lock. This relies on the rq->__lock order being in increasing CPU number (inside a core). It is also constrained to SMT8 per lockdep (and SMT256 per preempt_count). Luckily SMT8 is the max supported SMT count for Linux (Mips, Sparc and Power are known to have this). Signed-off-by:
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Peter Zijlstra authored
When switching on core-sched, CPUs need to agree which lock to use for their RQ. The new rule will be that rq->core_enabled will be toggled while holding all rq->__locks that belong to a core. This means we need to double check the rq->core_enabled value after each lock acquire and retry if it changed. This also has implications for those sites that take multiple RQ locks, they need to be careful that the second lock doesn't end up being the first lock. Verify the lock pointer after acquiring the first lock, because if they're on the same core, holding any of the rq->__lock instances will pin the core state. While there, change the rq->__lock order to CPU number, instead of rq address, this greatly simplifies the next patch. Signed-off-by:
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