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Subject[RFC PATCH v1 0/1] select idle cpu from idle cpumask in sched domain
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I'm writting to see if it makes sense to track idle cpus in a shared cpumask
in sched domain, then a task wakes up it can select idle cpu from this cpumask
instead of scanning all the cpus in the last level cache domain, especially
when the system is heavily loaded, the scanning cost could be significantly
reduced. The price is that the atomic cpumask ops are added to the idle entry
and exit paths.

I tested the following benchmarks on a x86 4 socket system with 24 cores per
socket and 2 hyperthreads per core, total 192 CPUs:

uperf throughput: netperf workload, tcp_nodelay, r/w size = 90

threads baseline-avg %std patch-avg %std
96 1 1.24 0.98 2.76
144 1 1.13 1.35 4.01
192 1 0.58 1.67 3.25
240 1 2.49 1.68 3.55

hackbench: process mode, 100000 loops, 40 file descriptors per group

group baseline-avg %std patch-avg %std
2(80) 1 12.05 0.97 9.88
3(120) 1 12.48 0.95 11.62
4(160) 1 13.83 0.97 13.22
5(200) 1 2.76 1.01 2.94

schbench: 99th percentile latency, 16 workers per message thread

mthread baseline-avg %std patch-avg %std
6(96) 1 1.24 0.993 1.73
9(144) 1 0.38 0.998 0.39
12(192) 1 1.58 0.995 1.64
15(240) 1 51.71 0.606 37.41

sysbench mysql throughput: read/write, table size = 10,000,000

thread baseline-avg %std patch-avg %std
96 1 1.77 1.015 1.71
144 1 3.39 0.998 4.05
192 1 2.88 1.002 2.81
240 1 2.07 1.011 2.09

kbuild: kexec reboot every time

baseline-avg patch-avg
1 1

Any suggestions are highly appreciated!

Thanks,
-Aubrey

Aubrey Li (1):
sched/fair: select idle cpu from idle cpumask in sched domain

include/linux/sched/topology.h | 13 +++++++++++++
kernel/sched/fair.c | 4 +++-
kernel/sched/topology.c | 2 +-
3 files changed, 17 insertions(+), 2 deletions(-)

--
2.25.1

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