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Subject[PATCH 00/10] sched/fair: wake_affine improvements
Date
Recently we found that some of the benchmark numbers on Power10 were lesser
than expected. Some analysis showed that the problem lies in the fact that
L2-Cache on Power10 is at core level i.e only 4 threads share the L2-cache.

One probable solution to the problem was worked by Gautham where he posted
http://lore.kernel.org/lkml/1617341874-1205-1-git-send-email-ego@linux.vnet.ibm.com/t/#u
a patch that marks MC domain as LLC.

Here the focus is on seeing if we can improve the current core scheduler's
wakeup mechanism by looking at idle-cores and nr_busy_cpus that is already
maintained per Last level cache(aka LLC) (first 8 patches) + explore the
possibility to provide a fallback LLC domain, that can be preferred if the
current LLC is busy (last 2 patches).

Except the last 2 patches, the rest patches should work independently of the
other proposed solution. i.e if the mc-llc patch is accepted, then the last
two patches may not be needed for Power10. However this may be helpful for
other archs/platforms.

In the fallback approach, we look for a one-to-one mapping for each LLC.
However this can be easily modified to look for all LLC's in the current
LLC's parent. Also fallback is only used for sync wakeups. This is because
that is where we expect the maximum benefit of moving the task closer to the
task. For non-sync wakeups, its expected that CPU from previous LLC may be
better off.

Request you to please review and provide your feedback.

Benchmarking numbers are from Power 10 but I have verified that we don't
regress on Power 9 setup.

# lscpu
Architecture: ppc64le
Byte Order: Little Endian
CPU(s): 80
On-line CPU(s) list: 0-79
Thread(s) per core: 8
Core(s) per socket: 10
Socket(s): 1
NUMA node(s): 1
Model: 1.0 (pvr 0080 0100)
Model name: POWER10 (architected), altivec supported
Hypervisor vendor: pHyp
Virtualization type: para
L1d cache: 64K
L1i cache: 32K
L2 cache: 256K
L3 cache: 8K
NUMA node2 CPU(s): 0-79

Hackbench: (latency, lower is better)

v5.12-rc5
instances = 1, min = 24.102529 usecs/op, median = usecs/op, max = 24.102529 usecs/op
instances = 2, min = 24.096112 usecs/op, median = 24.096112 usecs/op, max = 24.178903 usecs/op
instances = 4, min = 24.080541 usecs/op, median = 24.082990 usecs/op, max = 24.166873 usecs/op
instances = 8, min = 24.088969 usecs/op, median = 24.116081 usecs/op, max = 24.199853 usecs/op
instances = 16, min = 24.267228 usecs/op, median = 26.204510 usecs/op, max = 29.218360 usecs/op
instances = 32, min = 30.680071 usecs/op, median = 32.911664 usecs/op, max = 37.380470 usecs/op
instances = 64, min = 43.908331 usecs/op, median = 44.454343 usecs/op, max = 46.210298 usecs/op
instances = 80, min = 44.585754 usecs/op, median = 56.738546 usecs/op, max = 60.625826 usecs/op

v5.12-rc5 + mc-llc
instances = 1, min = 18.676505 usecs/op, median = usecs/op, max = 18.676505 usecs/op
instances = 2, min = 18.488627 usecs/op, median = 18.488627 usecs/op, max = 18.574946 usecs/op
instances = 4, min = 18.428399 usecs/op, median = 18.589051 usecs/op, max = 18.872548 usecs/op
instances = 8, min = 18.597389 usecs/op, median = 18.783815 usecs/op, max = 19.265532 usecs/op
instances = 16, min = 21.922350 usecs/op, median = 22.737792 usecs/op, max = 24.832429 usecs/op
instances = 32, min = 29.770446 usecs/op, median = 31.996687 usecs/op, max = 34.053042 usecs/op
instances = 64, min = 53.067842 usecs/op, median = 53.295139 usecs/op, max = 53.473059 usecs/op
instances = 80, min = 44.423288 usecs/op, median = 44.713767 usecs/op, max = 45.159761 usecs/op

v5.12-rc5 + this patchset
instances = 1, min = 19.368805 usecs/op, median = usecs/op, max = 19.368805 usecs/op
instances = 2, min = 19.423674 usecs/op, median = 19.423674 usecs/op, max = 19.506203 usecs/op
instances = 4, min = 19.454523 usecs/op, median = 19.596947 usecs/op, max = 19.863620 usecs/op
instances = 8, min = 20.005272 usecs/op, median = 20.239924 usecs/op, max = 20.878947 usecs/op
instances = 16, min = 21.856779 usecs/op, median = 24.102147 usecs/op, max = 25.496110 usecs/op
instances = 32, min = 31.460159 usecs/op, median = 32.809621 usecs/op, max = 33.939650 usecs/op
instances = 64, min = 39.506553 usecs/op, median = 43.835221 usecs/op, max = 45.645505 usecs/op
instances = 80, min = 43.805716 usecs/op, median = 44.314757 usecs/op, max = 48.910236 usecs/op

Summary:
mc-llc and this patchset seem to be performing much better than vanilla v5.12-rc5

DayTrader (throughput, higher is better)
v5.12-rc5 v5.12-rc5 v5.12-rc5
+ mc-llc + patchset
64CPUs/1JVM/ 60Users 6373.7 7520.5 7232.3
64CPUs/1JVM/ 80Users 6742.1 7940.9 7732.8
64CPUs/1JVM/100Users 6482.2 7730.3 7540
64CPUs/2JVM/ 60Users 6335 8081.6 7914.3
64CPUs/2JVM/ 80Users 6360.8 8259.6 8138.6
64CPUs/2JVM/100Users 6215.6 8046.5 8039.2
64CPUs/4JVM/ 60Users 5385.4 7685.3 7706.1
64CPUs/4JVM/ 80Users 5380.8 7753.3 7721.5
64CPUs/4JVM/100Users 5275.2 7549.2 7608.3

Summary: Across all profiles, this patchset or mc-llc out perform
vanilla v5.12-rc5
Not: Only 64 cores were online during this test.

schbench (latency: lesser is better)
======== Running schbench -m 3 -r 30 =================
Latency percentiles (usec) runtime 10 (s) (2545 total samples)
v5.12-rc5 | v5.12-rc5 + mc-llc | v5.12-rc5 + patchset

50.0th: 56 (1301 samples) | 50.0th: 49 (1309 samples) | 50.0th: 50 (1310 samples)
75.0th: 76 (623 samples) | 75.0th: 66 (628 samples) | 75.0th: 68 (632 samples)
90.0th: 93 (371 samples) | 90.0th: 78 (371 samples) | 90.0th: 80 (354 samples)
95.0th: 107 (123 samples) | 95.0th: 87 (117 samples) | 95.0th: 86 (126 samples)
*99.0th: 12560 (102 samples) *99.0th: 100 (97 samples) | *99.0th: 103 (97 samples)
99.5th: 15312 (14 samples) | 99.5th: 104 (12 samples) | 99.5th: 1202 (13 samples)
99.9th: 19936 (9 samples) | 99.9th: 106 (8 samples) | 99.9th: 14992 (10 samples)
min=13, max=20684 | min=15, max=113 | min=15, max=18721

Latency percentiles (usec) runtime 20 (s) (7649 total samples)

50.0th: 51 (3884 samples) | 50.0th: 50 (3935 samples) | 50.0th: 49 (3841 samples)
75.0th: 69 (1859 samples) | 75.0th: 66 (1817 samples) | 75.0th: 67 (1965 samples)
90.0th: 87 (1173 samples) | 90.0th: 80 (1204 samples) | 90.0th: 78 (1134 samples)
95.0th: 97 (368 samples) | 95.0th: 87 (342 samples) | 95.0th: 83 (359 samples)
*99.0th: 8624 (290 samples)| *99.0th: 98 (294 samples) | *99.0th: 93 (296 samples)
99.5th: 11344 (37 samples) | 99.5th: 102 (37 samples) | 99.5th: 98 (34 samples)
99.9th: 18592 (31 samples) | 99.9th: 106 (30 samples) | 99.9th: 7544 (28 samples)
min=13, max=20684 | min=12, max=113 | min=13, max=18721

Latency percentiles (usec) runtime 30 (s) (12785 total samples)

50.0th: 50 (6614 samples) | 50.0th: 49 (6544 samples) | 50.0th: 48 (6527 samples)
75.0th: 67 (3059 samples) | 75.0th: 65 (3100 samples) | 75.0th: 64 (3143 samples)
90.0th: 84 (1894 samples) | 90.0th: 79 (1912 samples) | 90.0th: 76 (1985 samples)
95.0th: 94 (586 samples) | 95.0th: 87 (646 samples) | 95.0th: 81 (585 samples)
*99.0th: 8304 (507 samples)| *99.0th: 101 (496 samples) | *99.0th: 90 (453 samples)
99.5th: 11696 (62 samples) | 99.5th: 104 (45 samples) | 99.5th: 94 (66 samples)
99.9th: 18592 (51 samples) | 99.9th: 110 (51 samples) | 99.9th: 1202 (49 samples)
min=12, max=21421 | min=1, max=126 | min=3, max=18721

Summary:
mc-llc is the best option, but this patchset also helps compared to vanilla v5.12-rc5


mongodb (threads=6) (throughput, higher is better)
Throughput read clean update
latency latency latency
v5.12-rc5 JVM=YCSB_CLIENTS=14 68116.05 ops/sec 1109.82 us 944.19 us 1342.29 us
v5.12-rc5 JVM=YCSB_CLIENTS=21 64802.69 ops/sec 1772.64 us 944.69 us 2099.57 us
v5.12-rc5 JVM=YCSB_CLIENTS=28 61792.78 ops/sec 2490.48 us 930.09 us 2928.03 us
v5.12-rc5 JVM=YCSB_CLIENTS=35 59604.44 ops/sec 3236.86 us 870.28 us 3787.48 us

v5.12-rc5 + mc-llc JVM=YCSB_CLIENTS=14 70948.51 ops/sec 1060.21 us 842.02 us 1289.44 us
v5.12-rc5 + mc-llc JVM=YCSB_CLIENTS=21 68732.48 ops/sec 1669.91 us 871.57 us 1975.19 us
v5.12-rc5 + mc-llc JVM=YCSB_CLIENTS=28 66674.81 ops/sec 2313.79 us 889.59 us 2702.36 us
v5.12-rc5 + mc-llc JVM=YCSB_CLIENTS=35 64397.51 ops/sec 3010.66 us 966.28 us 3484.19 us

v5.12-rc5 + patchset JVM=YCSB_CLIENTS=14 67403.29 ops/sec 1121.80 us 797.81 us 1357.28 us
v5.12-rc5 + patchset JVM=YCSB_CLIENTS=21 63952.79 ops/sec 1792.86 us 779.59 us 2130.54 us
v5.12-rc5 + patchset JVM=YCSB_CLIENTS=28 62198.83 ops/sec 2469.60 us 780.00 us 2914.48 us
v5.12-rc5 + patchset JVM=YCSB_CLIENTS=35 60333.81 ops/sec 3192.41 us 822.09 us 3748.24 us

Summary:
mc-llc outperforms, this patchset and upstream almost give similar performance.


Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Parth Shah <parth@linux.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Rik van Riel <riel@surriel.com>

Srikar Dronamraju (10):
sched/fair: Update affine statistics when needed
sched/fair: Maintain the identity of idle-core
sched/fair: Update idle-core more often
sched/fair: Prefer idle CPU to cache affinity
sched/fair: Call wake_affine only if necessary
sched/idle: Move busy_cpu accounting to idle callback
sched/fair: Remove ifdefs in waker_affine_idler_llc
sched/fair: Dont iterate if no idle CPUs
sched/topology: Introduce fallback LLC
powerpc/smp: Add fallback flag to powerpc MC domain

arch/powerpc/kernel/smp.c | 7 +-
include/linux/sched/sd_flags.h | 7 +
include/linux/sched/topology.h | 3 +-
kernel/sched/fair.c | 229 +++++++++++++++++++++++++++------
kernel/sched/features.h | 1 +
kernel/sched/idle.c | 33 ++++-
kernel/sched/sched.h | 6 +
kernel/sched/topology.c | 54 +++++++-
8 files changed, 296 insertions(+), 44 deletions(-)

--
2.18.2

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