• Rohit Jain's avatar
    sched/core: Don't schedule threads on pre-empted vCPUs · 247f2f6f
    Rohit Jain authored
    In paravirt configurations today, spinlocks figure out whether a vCPU is
    running to determine whether or not spinlock should bother spinning. We
    can use the same logic to prioritize CPUs when scheduling threads. If a
    vCPU has been pre-empted, it will incur the extra cost of VMENTER and
    the time it actually spends to be running on the host CPU. If we had
    other vCPUs which were actually running on the host CPU and idle we
    should schedule threads there.
    
    Performance numbers:
    
    Note: With patch is referred to as Paravirt in the following and without
    patch is referred to as Base.
    
    1) When only 1 VM is running:
    
        a) Hackbench test on KVM 8 vCPUs, 10,000 loops (lower is better):
    
    	+-------+-----------------+----------------+
    	|Number |Paravirt         |Base            |
    	|of     +---------+-------+-------+--------+
    	|Threads|Average  |Std Dev|Average| Std Dev|
    	+-------+---------+-------+-------+--------+
    	|1      |1.817    |0.076  |1.721  | 0.067  |
    	|2      |3.467    |0.120  |3.468  | 0.074  |
    	|4      |6.266    |0.035  |6.314  | 0.068  |
    	|8      |11.437   |0.105  |11.418 | 0.132  |
    	|16     |21.862   |0.167  |22.161 | 0.129  |
    	|25     |33.341   |0.326  |33.692 | 0.147  |
    	+-------+---------+-------+-------+--------+
    
    2) When two VMs are running with same CPU affinities:
    
        a) tbench test on VM 8 cpus
    
        Base:
    
    	VM1:
    
    	Throughput 220.59 MB/sec   1 clients  1 procs  max_latency=12.872 ms
    	Throughput 448.716 MB/sec  2 clients  2 procs  max_latency=7.555 ms
    	Throughput 861.009 MB/sec  4 clients  4 procs  max_latency=49.501 ms
    	Throughput 1261.81 MB/sec  7 clients  7 procs  max_latency=76.990 ms
    
    	VM2:
    
    	Throughput 219.937 MB/sec  1 clients  1 procs  max_latency=12.517 ms
    	Throughput 470.99 MB/sec   2 clients  2 procs  max_latency=12.419 ms
    	Throughput 841.299 MB/sec  4 clients  4 procs  max_latency=37.043 ms
    	Throughput 1240.78 MB/sec  7 clients  7 procs  max_latency=77.489 ms
    
        Paravirt:
    
    	VM1:
    
    	Throughput 222.572 MB/sec  1 clients  1 procs  max_latency=7.057 ms
    	Throughput 485.993 MB/sec  2 clients  2 procs  max_latency=26.049 ms
    	Throughput 947.095 MB/sec  4 clients  4 procs  max_latency=45.338 ms
    	Throughput 1364.26 MB/sec  7 clients  7 procs  max_latency=145.124 ms
    
    	VM2:
    
    	Throughput 224.128 MB/sec  1 clients  1 procs  max_latency=4.564 ms
    	Throughput 501.878 MB/sec  2 clients  2 procs  max_latency=11.061 ms
    	Throughput 965.455 MB/sec  4 clients  4 procs  max_latency=45.370 ms
    	Throughput 1359.08 MB/sec  7 clients  7 procs  max_latency=168.053 ms
    
        b) Hackbench with 4 fd 1,000,000 loops
    
    	+-------+--------------------------------------+----------------------------------------+
    	|Number |Paravirt                              |Base                                    |
    	|of     +----------+--------+---------+--------+----------+--------+---------+----------+
    	|Threads|Average1  |Std Dev1|Average2 | Std Dev|Average1  |Std Dev1|Average2 | Std Dev 2|
    	+-------+----------+--------+---------+--------+----------+--------+---------+----------+
    	|  1    | 3.748    | 0.620  | 3.576   | 0.432  | 4.006    | 0.395  | 3.446   | 0.787    |
    	+-------+----------+--------+---------+--------+----------+--------+---------+----------+
    
        Note that this test was run just to show the interference effect
        over-subscription can have in baseline
    
        c) schbench results with 2 message groups on 8 vCPU VMs
    
    	+-----------+-------+---------------+--------------+------------+
    	|           |       | Paravirt      | Base         |            |
    	+-----------+-------+-------+-------+-------+------+------------+
    	|           |Threads| VM1   | VM2   |  VM1  | VM2  |%Improvement|
    	+-----------+-------+-------+-------+-------+------+------------+
    	|50.0000th  |    1  | 52    | 53    |  58   | 54   |  +6.25%    |
    	|75.0000th  |    1  | 69    | 61    |  83   | 59   |  +8.45%    |
    	|90.0000th  |    1  | 80    | 80    |  89   | 83   |  +6.98%    |
    	|95.0000th  |    1  | 83    | 83    |  93   | 87   |  +7.78%    |
    	|*99.0000th |    1  | 92    | 94    |  99   | 97   |  +5.10%    |
    	|99.5000th  |    1  | 95    | 100   |  102  | 103  |  +4.88%    |
    	|99.9000th  |    1  | 107   | 123   |  105  | 203  |  +25.32%   |
    	+-----------+-------+-------+-------+-------+------+------------+
    	|50.0000th  |    2  | 56    | 62    |  67   | 59   |  +6.35%    |
    	|75.0000th  |    2  | 69    | 75    |  80   | 71   |  +4.64%    |
    	|90.0000th  |    2  | 80    | 82    |  90   | 81   |  +5.26%    |
    	|95.0000th  |    2  | 85    | 87    |  97   | 91   |  +8.51%    |
    	|*99.0000th |    2  | 98    | 99    |  107  | 109  |  +8.79%    |
    	|99.5000th  |    2  | 107   | 105   |  109  | 116  |  +5.78%    |
    	|99.9000th  |    2  | 9968  | 609   |  875  | 3116 | -165.02%   |
    	+-----------+-------+-------+-------+-------+------+------------+
    	|50.0000th  |    4  | 78    | 77    |  78   | 79   |  +1.27%    |
    	|75.0000th  |    4  | 98    | 106   |  100  | 104  |   0.00%    |
    	|90.0000th  |    4  | 987   | 1001  |  995  | 1015 |  +1.09%    |
    	|95.0000th  |    4  | 4136  | 5368  |  5752 | 5192 |  +13.16%   |
    	|*99.0000th |    4  | 11632 | 11344 |  11024| 10736|  -5.59%    |
    	|99.5000th  |    4  | 12624 | 13040 |  12720| 12144|  -3.22%    |
    	|99.9000th  |    4  | 13168 | 18912 |  14992| 17824|  +2.24%    |
    	+-----------+-------+-------+-------+-------+------+------------+
    
        Note: Improvement is measured for (VM1+VM2)
    Signed-off-by: default avatarRohit Jain <rohit.k.jain@oracle.com>
    Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: dhaval.giani@oracle.com
    Cc: matt@codeblueprint.co.uk
    Cc: steven.sistare@oracle.com
    Cc: subhra.mazumdar@oracle.com
    Link: http://lkml.kernel.org/r/1525294330-7759-1-git-send-email-rohit.k.jain@oracle.comSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
    247f2f6f
core.c 174 KB