- 02 Jul, 2010 7 commits
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Tejun Heo authored
This patch implements unbound workqueue which can be specified with WQ_UNBOUND flag on creation. An unbound workqueue has the following properties. * It uses a dedicated gcwq with a pseudo CPU number WORK_CPU_UNBOUND. This gcwq is always online and disassociated. * Workers are not bound to any CPU and not concurrency managed. Works are dispatched to workers as soon as possible and the only applied limitation is @max_active. IOW, all unbound workqeueues are implicitly high priority. Unbound workqueues can be used as simple execution context provider. Contexts unbound to any cpu are served as soon as possible. Signed-off-by:Tejun Heo <tj@kernel.org> Cc: Arjan van de Ven <arjan@linux.intel.com> Cc: David Howells <dhowells@redhat.com>
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Tejun Heo authored
In preparation of WQ_UNBOUND addition, make the following changes. * Add WORK_CPU_* constants for pseudo cpu id numbers used (currently only WORK_CPU_NONE) and use them instead of NR_CPUS. This is to allow another pseudo cpu id for unbound cpu. * Reorder WQ_* flags. * Make workqueue_struct->cpu_wq a union which contains a percpu pointer, regular pointer and an unsigned long value and use kzalloc/kfree() in UP allocation path. This will be used to implement unbound workqueues which will use only one cwq on SMPs. * Move alloc_cwqs() allocation after initialization of wq fields, so that alloc_cwqs() has access to wq->flags. * Trivial relocation of wq local variables in freeze functions. These changes don't cause any functional change. Signed-off-by: -
Tejun Heo authored
libata has two concurrency related limitations. a. ata_wq which is used for polling PIO has single thread per CPU. If there are multiple devices doing polling PIO on the same CPU, they can't be executed simultaneously. b. ata_aux_wq which is used for SCSI probing has single thread. In cases where SCSI probing is stalled for extended period of time which is possible for ATAPI devices, this will stall all probing. #a is solved by increasing maximum concurrency of ata_wq. Please note that polling PIO might be used under allocation path and thus needs to be served by a separate wq with a rescuer. #b is solved by using the default wq instead and achieving exclusion via per-port mutex. Signed-off-by:
Jeff Garzik <jgarzik@pobox.com>
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Tejun Heo authored
When there's no pending work to do, worker_thread() goes back to sleep after waking up without checking whether worker management is necessary. This means that idle worker exit requests can be ignored if the gcwq stays empty. Fix it by making worker_thread() always check whether worker management is necessary before going to sleep. Signed-off-by: -
Tejun Heo authored
get_work_gcwq() was incorrectly triggering BUG_ON() if cpu number is equal to or higher than num_possible_cpus() instead of nr_cpu_ids. Fix it. Signed-off-by: -
Tejun Heo authored
When one flusher is cascading to the next flusher, it first sets wq->first_flusher to the next one and sets up the next flush cycle. If there's nothing to do for the next cycle, it clears wq->flush_flusher and proceeds to the one after that. If the woken up flusher checks wq->first_flusher before it gets cleared, it will incorrectly assume the role of the first flusher, which triggers BUG_ON() sanity check. Fix it by checking wq->first_flusher again after grabbing the mutex. Signed-off-by: -
Tejun Heo authored
worker_set/clr_flags() assume that if none of NOT_RUNNING flags is set the worker must be contributing to nr_running which is only true if the worker is actually running. As when called from self, it is guaranteed that the worker is running, those functions can be safely used from the worker itself and they aren't necessary from other places anyway. Make the following changes to fix the bug. * Make worker_set/clr_flags() whine if not called from self. * Convert all places which called those functions from other tasks to manipulate flags directly. * Make trustee_thread() directly clear nr_running after setting WORKER_ROGUE on all workers. This is the only place where nr_running manipulation is necessary outside of workers themselves. * While at it, add sanity check for nr_running in worker_enter_idle(). Signed-off-by:
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- 29 Jun, 2010 32 commits
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Tejun Heo authored
This patch implements cpu intensive workqueue which can be specified with WQ_CPU_INTENSIVE flag on creation. Works queued to a cpu intensive workqueue don't participate in concurrency management. IOW, it doesn't contribute to gcwq->nr_running and thus doesn't delay excution of other works. Note that although cpu intensive works won't delay other works, they can be delayed by other works. Combine with WQ_HIGHPRI to avoid being delayed by other works too. As the name suggests this is useful when using workqueue for cpu intensive works. Workers executing cpu intensive works are not considered for workqueue concurrency management and left for the scheduler to manage. Signed-off-by: -
Tejun Heo authored
This patch implements high priority workqueue which can be specified with WQ_HIGHPRI flag on creation. A high priority workqueue has the following properties. * A work queued to it is queued at the head of the worklist of the respective gcwq after other highpri works, while normal works are always appended at the end. * As long as there are highpri works on gcwq->worklist, [__]need_more_worker() remains %true and process_one_work() wakes up another worker before it start executing a work. The above two properties guarantee that works queued to high priority workqueues are dispatched to workers and start execution as soon as possible regardless of the state of other works. Signed-off-by: -
Tejun Heo authored
Implement the following utility APIs. workqueue_set_max_active() : adjust max_active of a wq workqueue_congested() : test whether a wq is contested work_cpu() : determine the last / current cpu of a work work_busy() : query whether a work is busy * Anton Blanchard fixed missing ret initialization in work_busy(). Signed-off-by: -
Tejun Heo authored
This patch makes changes to make new workqueue features available to its users. * Now that workqueue is more featureful, there should be a public workqueue creation function which takes paramters to control them. Rename __create_workqueue() to alloc_workqueue() and make 0 max_active mean WQ_DFL_ACTIVE. In the long run, all create_workqueue_*() will be converted over to alloc_workqueue(). * To further unify access interface, rename keventd_wq to system_wq and export it. * Add system_long_wq and system_nrt_wq. The former is to host long running works separately (so that flush_scheduled_work() dosen't take so long) and the latter guarantees any queued work item is never executed in parallel by multiple CPUs. These will be used by future patches to update workqueue users. Signed-off-by: -
Tejun Heo authored
Define WQ_MAX_ACTIVE and create keventd with max_active set to half of it which means that keventd now can process upto WQ_MAX_ACTIVE / 2 - 1 works concurrently. Unless some combination can result in dependency loop longer than max_active, deadlock won't happen and thus it's unnecessary to check whether current_is_keventd() before trying to schedule a work. Kill current_is_keventd(). (Lockdep annotations are broken. We need lock_map_acquire_read_norecurse()) Signed-off-by: -
Tejun Heo authored
Instead of creating a worker for each cwq and putting it into the shared pool, manage per-cpu workers dynamically. Works aren't supposed to be cpu cycle hogs and maintaining just enough concurrency to prevent work processing from stalling due to lack of processing context is optimal. gcwq keeps the number of concurrent active workers to minimum but no less. As long as there's one or more running workers on the cpu, no new worker is scheduled so that works can be processed in batch as much as possible but when the last running worker blocks, gcwq immediately schedules new worker so that the cpu doesn't sit idle while there are works to be processed. gcwq always keeps at least single idle worker around. When a new worker is necessary and the worker is the last idle one, the worker assumes the role of "manager" and manages the worker pool - ie. creates another worker. Forward-progress is guaranteed by having dedicated rescue workers for workqueues which may be necessary while creating a new worker. When the manager is having problem creating a new worker, mayday timer activates and rescue workers are summoned to the cpu and execute works which might be necessary to create new workers. Trustee is expanded to serve the role of manager while a CPU is being taken down and stays down. As no new works are supposed to be queued on a dead cpu, it just needs to drain all the existing ones. Trustee continues to try to create new workers and summon rescuers as long as there are pending works. If the CPU is brought back up while the trustee is still trying to drain the gcwq from the previous offlining, the trustee will kill all idles ones and tell workers which are still busy to rebind to the cpu, and pass control over to gcwq which assumes the manager role as necessary. Concurrency managed worker pool reduces the number of workers drastically. Only workers which are necessary to keep the processing going are created and kept. Also, it reduces cache footprint by avoiding unnecessarily switching contexts between different workers. Please note that this patch does not increase max_active of any workqueue. All workqueues can still only process one work per cpu. Signed-off-by: -
Tejun Heo authored
Implement worker_{set|clr}_flags() to manipulate worker flags. These are currently simple wrappers but logics to track the current worker state and the current level of concurrency will be added. Signed-off-by: -
Tejun Heo authored
Use gcwq->worklist instead of cwq->worklist and break the strict association between a cwq and its worker. All works queued on a cpu are queued on gcwq->worklist and processed by any available worker on the gcwq. As there no longer is strict association between a cwq and its worker, whether a work is executing can now only be determined by calling [__]find_worker_executing_work(). After this change, the only association between a cwq and its worker is that a cwq puts a worker into shared worker pool on creation and kills it on destruction. As all workqueues are still limited to max_active of one, this means that there are always at least as many workers as active works and thus there's no danger for deadlock. The break of strong association between cwqs and workers requires somewhat clumsy changes to current_is_keventd() and destroy_workqueue(). Dynamic worker pool management will remove both clumsy changes. current_is_keventd() won't be necessary at all as the only reason it exists is to avoid queueing a work from a work which will be allowed just fine. The clumsy part of destroy_workqueue() is added because a worker can only be destroyed while idle and there's no guarantee a worker is idle when its wq is going down. With dynamic pool management, workers are not associated with workqueues at all and only idle ones will be submitted to destroy_workqueue() so the code won't be necessary anymore. Signed-off-by: -
Tejun Heo authored
With gcwq managing all the workers and work->data pointing to the last gcwq it was on, non-reentrance can be easily implemented by checking whether the work is still running on the previous gcwq on queueing. Implement it. Signed-off-by: -
Tejun Heo authored
To implement non-reentrant workqueue, the last gcwq a work was executed on must be reliably obtainable as long as the work structure is valid even if the previous workqueue has been destroyed. To achieve this, work->data will be overloaded to carry the last cpu number once execution starts so that the previous gcwq can be located reliably. This means that cwq can't be obtained from work after execution starts but only gcwq. Implement set_work_{cwq|cpu}(), get_work_[g]cwq() and clear_work_data() to set work data to the cpu number when starting execution, access the overloaded work data and clear it after cancellation. queue_delayed_work_on() is updated to preserve the last cpu while in-flight in timer and other callers which depended on getting cwq from work after execution starts are converted to depend on gcwq instead. * Anton Blanchard fixed compile error on powerpc due to missing linux/threads.h include. Signed-off-by: -
Tejun Heo authored
Now that all the workers are tracked by gcwq, we can find which worker is executing a work from gcwq. Implement find_worker_executing_work() and make worker track its current_cwq so that we can find things the other way around. This will be used to implement non-reentrant wqs. Signed-off-by: -
Tejun Heo authored
Reimplement st (single thread) workqueue so that it's friendly to shared worker pool. It was originally implemented by confining st workqueues to use cwq of a fixed cpu and always having a worker for the cpu. This implementation isn't very friendly to shared worker pool and suboptimal in that it ends up crossing cpu boundaries often. Reimplement st workqueue using dynamic single cpu binding and cwq->limit. WQ_SINGLE_THREAD is replaced with WQ_SINGLE_CPU. In a single cpu workqueue, at most single cwq is bound to the wq at any given time. Arbitration is done using atomic accesses to wq->single_cpu when queueing a work. Once bound, the binding stays till the workqueue is drained. Note that the binding is never broken while a workqueue is frozen. This is because idle cwqs may have works waiting in delayed_works queue while frozen. On thaw, the cwq is restarted if there are any delayed works or unbound otherwise. When combined with max_active limit of 1, single cpu workqueue has exactly the same execution properties as the original single thread workqueue while allowing sharing of per-cpu workers. Signed-off-by: -
Tejun Heo authored
Reimplement CPU hotplugging support using trustee thread. On CPU down, a trustee thread is created and each step of CPU down is executed by the trustee and workqueue_cpu_callback() simply drives and waits for trustee state transitions. CPU down operation no longer waits for works to be drained but trustee sticks around till all pending works have been completed. If CPU is brought back up while works are still draining, workqueue_cpu_callback() tells trustee to step down and tell workers to rebind to the cpu. As it's difficult to tell whether cwqs are empty if it's freezing or frozen, trustee doesn't consider draining to be complete while a gcwq is freezing or frozen (tracked by new GCWQ_FREEZING flag). Also, workers which get unbound from their cpu are marked with WORKER_ROGUE. Trustee based implementation doesn't bring any new feature at this point but it will be used to manage worker pool when dynamic shared worker pool is implemented. Signed-off-by: -
Tejun Heo authored
Implement worker states. After created, a worker is STARTED. While a worker isn't processing a work, it's IDLE and chained on gcwq->idle_list. While processing a work, a worker is BUSY and chained on gcwq->busy_hash. Also, gcwq now counts the number of all workers and idle ones. worker_thread() is restructured to reflect state transitions. cwq->more_work is removed and waking up a worker makes it check for events. A worker is killed by setting DIE flag while it's IDLE and waking it up. This gives gcwq better visibility of what's going on and allows it to find out whether a work is executing quickly which is necessary to have multiple workers processing the same cwq. Signed-off-by: -
Tejun Heo authored
There is one gcwq (global cwq) per each cpu and all cwqs on an cpu point to it. A gcwq contains a lock to be used by all cwqs on the cpu and an ida to give IDs to workers belonging to the cpu. This patch introduces gcwq, moves worker_ida into gcwq and make all cwqs on the same cpu use the cpu's gcwq->lock instead of separate locks. gcwq->ida is now protected by gcwq->lock too. Signed-off-by: -
Tejun Heo authored
Currently, workqueue freezing is implemented by marking the worker freezeable and calling try_to_freeze() from dispatch loop. Reimplement it using cwq->limit so that the workqueue is frozen instead of the worker. * workqueue_struct->saved_max_active is added which stores the specified max_active on initialization. * On freeze, all cwq->max_active's are quenched to zero. Freezing is complete when nr_active on all cwqs reach zero. * On thaw, all cwq->max_active's are restored to wq->saved_max_active and the worklist is repopulated. This new implementation allows having single shared pool of workers per cpu. Signed-off-by: -
Tejun Heo authored
Add cwq->nr_active, cwq->max_active and cwq->delayed_work. nr_active counts the number of active works per cwq. A work is active if it's flushable (colored) and is on cwq's worklist. If nr_active reaches max_active, new works are queued on cwq->delayed_work and activated later as works on the cwq complete and decrement nr_active. cwq->max_active can be specified via the new @max_active parameter to __create_workqueue() and is set to 1 for all workqueues for now. As each cwq has only single worker now, this double queueing doesn't cause any behavior difference visible to its users. This will be used to reimplement freeze/thaw and implement shared worker pool. Signed-off-by: -
Tejun Heo authored
A work is linked to the next one by having WORK_STRUCT_LINKED bit set and these links can be chained. When a linked work is dispatched to a worker, all linked works are dispatched to the worker's newly added ->scheduled queue and processed back-to-back. Currently, as there's only single worker per cwq, having linked works doesn't make any visible behavior difference. This change is to prepare for multiple shared workers per cpu. Signed-off-by: -
Tejun Heo authored
Separate out worker thread related information to struct worker from struct cpu_workqueue_struct and implement helper functions to deal with the new struct worker. The only change which is visible outside is that now workqueue worker are all named "kworker/CPUID:WORKERID" where WORKERID is allocated from per-cpu ida. This is in preparation of concurrency managed workqueue where shared multiple workers would be available per cpu. Signed-off-by: -
Tejun Heo authored
Reimplement workqueue flushing using color coded works. wq has the current work color which is painted on the works being issued via cwqs. Flushing a workqueue is achieved by advancing the current work colors of cwqs and waiting for all the works which have any of the previous colors to drain. Currently there are 16 possible colors, one is reserved for no color and 15 colors are useable allowing 14 concurrent flushes. When color space gets full, flush attempts are batched up and processed together when color frees up, so even with many concurrent flushers, the new implementation won't build up huge queue of flushers which has to be processed one after another. Only works which are queued via __queue_work() are colored. Works which are directly put on queue using insert_work() use NO_COLOR and don't participate in workqueue flushing. Currently only works used for work-specific flush fall in this category. This new implementation leaves only cleanup_workqueue_thread() as the user of flush_cpu_workqueue(). Just make its users use flush_workqueue() and kthread_stop() directly and kill cleanup_workqueue_thread(). As workqueue flushing doesn't use barrier request anymore, the comment describing the complex synchronization around it in cleanup_workqueue_thread() is removed together with the function. This new implementation is to allow having and sharing multiple workers per cpu. Please note that one more bit is reserved for a future work flag by this patch. This is to avoid shifting bits and updating comments later. Signed-off-by: -
Tejun Heo authored
work->data field is used for two purposes. It points to cwq it's queued on and the lower bits are used for flags. Currently, two bits are reserved which is always safe as 4 byte alignment is guaranteed on every architecture. However, future changes will need more flag bits. On SMP, the percpu allocator is capable of honoring larger alignment (there are other users which depend on it) and larger alignment works just fine. On UP, percpu allocator is a thin wrapper around kzalloc/kfree() and don't honor alignment request. This patch introduces WORK_STRUCT_FLAG_BITS and implements alloc/free_cwqs() which guarantees max(1 << WORK_STRUCT_FLAG_BITS, __alignof__(unsigned long long) alignment both on SMP and UP. On SMP, simply wrapping percpu allocator is enough. On UP, extra space is allocated so that cwq can be aligned and the original pointer can be stored after it which is used in the free path. * Alignment problem on UP is reported by Michal Simek. Signed-off-by:
Michal Simek <michal.simek@petalogix.com>
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Tejun Heo authored
Worker management is about to be overhauled. Simplify things by removing cpu_populated_map, creating workers for all possible cpus and making single threaded workqueues behave more like multi threaded ones. After this patch, all cwqs are always initialized, all workqueues are linked on the workqueues list and workers for all possibles cpus always exist. This also makes CPU hotplug support simpler - checking ->cpus_allowed before processing works in worker_thread() and flushing cwqs on CPU_POST_DEAD are enough. While at it, make get_cwq() always return the cwq for the specified cpu, add target_cwq() for cases where single thread distinction is necessary and drop all direct usage of per_cpu_ptr() on wq->cpu_wq. Signed-off-by: -
Tejun Heo authored
Strip tracing code from workqueue and remove workqueue tracing. This is temporary measure till concurrency managed workqueue is complete. Signed-off-by: -
Tejun Heo authored
Separate out process_one_work() out of run_workqueue(). This patch doesn't cause any behavior change. Signed-off-by: -
Tejun Heo authored
Work flags are about to see more traditional mask handling. Define WORK_STRUCT_*_BIT as the bit position constant and redefine WORK_STRUCT_* as bit masks. Also, make WORK_STRUCT_STATIC_* flags conditional While at it, re-define these constants as enums and use WORK_STRUCT_STATIC instead of hard-coding 2 in WORK_DATA_STATIC_INIT(). Signed-off-by: -
Tejun Heo authored
Currently, __create_workqueue_key() takes @singlethread and @freezeable paramters and store them separately in workqueue_struct. Merge them into a single flags parameter and field and use WQ_FREEZEABLE and WQ_SINGLE_THREAD. Signed-off-by: -
Tejun Heo authored
Make the following updates in preparation of concurrency managed workqueue. None of these changes causes any visible behavior difference. * Add comments and adjust indentations to data structures and several functions. * Rename wq_per_cpu() to get_cwq() and swap the position of two parameters for consistency. Convert a direct per_cpu_ptr() access to wq->cpu_wq to get_cwq(). * Add work_static() and Update set_wq_data() such that it sets the flags part to WORK_STRUCT_PENDING | WORK_STRUCT_STATIC if static | @extra_flags. * Move santiy check on work->entry emptiness from queue_work_on() to __queue_work() which all queueing paths share. * Make __queue_work() take @cpu and @wq instead of @cwq. * Restructure flush_work() and __create_workqueue_key() to make them easier to modify. Signed-off-by: -
Tejun Heo authored
With stop_machine() converted to use cpu_stop, RT workqueue doesn't have any user left. Kill RT workqueue support. Signed-off-by: -
Tejun Heo authored
ACPI works need to be executed on cpu0 and acpi/osl.c achieves this by creating singlethread workqueue and then binding it to cpu0 from a work which is quite unorthodox. Make it create regular workqueues and use queue_work_on() instead. This is in preparation of concurrency managed workqueue and the extra workers won't be a problem after it's implemented. Signed-off-by: -
Tejun Heo authored
Implement kthread_data() which takes @task pointing to a kthread and returns @data specified when creating the kthread. The caller is responsible for ensuring the validity of @task when calling this function. Signed-off-by: -
Tejun Heo authored
Upcoming workqueue updates will no longer guarantee fixed workqueue to worker kthread association, so giving RT priority to the irq worker won't work. Use kthread_worker which guarantees specific kthread association instead. This also makes setting the priority cleaner. Signed-off-by: -
Tejun Heo authored
Implement simple work processor for kthread. This is to ease using kthread. Single thread workqueue used to be used for things like this but workqueue won't guarantee fixed kthread association anymore to enable worker sharing. This can be used in cases where specific kthread association is necessary, for example, when it should have RT priority or be assigned to certain cgroup. Signed-off-by:
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- 13 Jun, 2010 1 commit
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Tejun Heo authored
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