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SubjectRe: [PATCH] x86,sched: Fix sched_smt_power_savings totally broken
On Mon, Jan 09, 2012 at 04:56:07PM +0800, Youquan Song wrote:
> sched_smt_power_savings is totally broken at lastest linux and -tip tree.
>
> sched_smt_power_savings is set to 1, the scheduler tries to schedule processes
> on the least number of hyper-threads on a core as possible. In other words,
> the process load is distributed such that all the hyper-threads in a core and
> all the cores within the same processor are busy before the load is distributed
> to other hyper-threads and cores in another processor.
>
> Test On Intel Xeon machine with 2 physical CPUs and each CPU has 8 cores / 16
> threads. physical CPU 0 includes cpu[0~7] and cpu[16~23]; while physical CPU 1
> includes cpu[8~15] and cpu[24~31].
>
> At latest -tip tree:
> echo 1 > /sys/devices/system/cpu/sched_smt_power_savings
> ./ebizzy -t 16 -S 100 & sleep 10 ; cat /proc/sched_debug | grep -A 1 cpu# > tmp.log
>
> cpu#0, 2693.564 MHz
> .nr_running : 0
> --
> cpu#1, 2693.564 MHz
> .nr_running : 1
> --
> cpu#2, 2693.564 MHz
> .nr_running : 0
> --
> cpu#3, 2693.564 MHz
> .nr_running : 1
> --
> cpu#4, 2693.564 MHz
> .nr_running : 1
> --
> cpu#5, 2693.564 MHz
> .nr_running : 1
> --
> cpu#6, 2693.564 MHz
> .nr_running : 1
> --
> cpu#7, 2693.564 MHz
> .nr_running : 1
> --
> cpu#8, 2693.564 MHz
> .nr_running : 1
> --
> cpu#9, 2693.564 MHz
> .nr_running : 1
> --
> cpu#10, 2693.564 MHz
> .nr_running : 1
> --
> cpu#11, 2693.564 MHz
> .nr_running : 0
> --
> cpu#12, 2693.564 MHz
> .nr_running : 1
> --
> cpu#13, 2693.564 MHz
> .nr_running : 1
> --
> cpu#14, 2693.564 MHz
> .nr_running : 0
> --
> cpu#15, 2693.564 MHz
> .nr_running : 0
> --
> cpu#16, 2693.564 MHz
> .nr_running : 0
> --
> cpu#17, 2693.564 MHz
> .nr_running : 0
> --
> cpu#18, 2693.564 MHz
> .nr_running : 1
> --
> cpu#19, 2693.564 MHz
> .nr_running : 0
> --
> cpu#20, 2693.564 MHz
> .nr_running : 0
> --
> cpu#21, 2693.564 MHz
> .nr_running : 0
> --
> cpu#22, 2693.564 MHz
> .nr_running : 0
> --
> cpu#23, 2693.564 MHz
> .nr_running : 0
> --
> cpu#24, 2693.564 MHz
> .nr_running : 0
> --
> cpu#25, 2693.564 MHz
> .nr_running : 1
> --
> cpu#26, 2693.564 MHz
> .nr_running : 1
> --
> cpu#27, 2693.564 MHz
> .nr_running : 1
> --
> cpu#28, 2693.564 MHz
> .nr_running : 0
> --
> cpu#29, 2693.564 MHz
> .nr_running : 0
> --
> cpu#30, 2693.564 MHz
> .nr_running : 1
> --
> cpu#31, 2693.564 MHz
> .nr_running : 1
>
> >From above, we notice 16 threads are distributed among 2 physical CPUs.
> After apply the patch, 16 threads are only distributed at one physical CPU.
> In this case, we can notice 30% power saving.
> Following are the result after apply the patch:
>
> cpu#0, 2693.384 MHz
> .nr_running : 1
> --
> cpu#1, 2693.384 MHz
> .nr_running : 1
> --
> cpu#2, 2693.384 MHz
> .nr_running : 1
> --
> cpu#3, 2693.384 MHz
> .nr_running : 1
> --
> cpu#4, 2693.384 MHz
> .nr_running : 1
> --
> cpu#5, 2693.384 MHz
> .nr_running : 1
> --
> cpu#6, 2693.384 MHz
> .nr_running : 1
> --
> cpu#7, 2693.384 MHz
> .nr_running : 1
> --
> cpu#8, 2693.384 MHz
> .nr_running : 0
> --
> cpu#9, 2693.384 MHz
> .nr_running : 0
> --
> cpu#10, 2693.384 MHz
> .nr_running : 0
> --
> cpu#11, 2693.384 MHz
> .nr_running : 0
> --
> cpu#12, 2693.384 MHz
> .nr_running : 0
> --
> cpu#13, 2693.384 MHz
> .nr_running : 0
> --
> cpu#14, 2693.384 MHz
> .nr_running : 0
> --
> cpu#15, 2693.384 MHz
> .nr_running : 0
> --
> cpu#16, 2693.384 MHz
> .nr_running : 1
> --
> cpu#17, 2693.384 MHz
> .nr_running : 1
> --
> cpu#18, 2693.384 MHz
> .nr_running : 1
> --
> cpu#19, 2693.384 MHz
> .nr_running : 1
> --
> cpu#20, 2693.384 MHz
> .nr_running : 1
> --
> cpu#21, 2693.384 MHz
> .nr_running : 1
> --
> cpu#22, 2693.384 MHz
> .nr_running : 1
> --
> cpu#23, 2693.384 MHz
> .nr_running : 1
> --
> cpu#24, 2693.384 MHz
> .nr_running : 0
> --
> cpu#25, 2693.384 MHz
> .nr_running : 0
> --
> cpu#26, 2693.384 MHz
> .nr_running : 0
> --
> cpu#27, 2693.384 MHz
> .nr_running : 0
> --
> cpu#28, 2693.384 MHz
> .nr_running : 0
> --
> cpu#29, 2693.384 MHz
> .nr_running : 0
> --
> cpu#30, 2693.384 MHz
> .nr_running : 0
> --
> cpu#31, 2693.384 MHz
> .nr_running : 1
>
>
> This patch will set SMT sibling power capability to SCHED_POWER_SCALE
> (1024) when sched_smt_power_savings set. So when there is possible do power
> saving during scheduling, scheduler will truly schedule processes as
> sched_smt_power_savings should do.
>
>
> Signed-off-by: Youquan Song <youquan.song@intel.com>
> Tested-by: Anhua Xu <anhua.xu@intel.com>
> ---
> kernel/sched/fair.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read Documentation/stable_kernel_rules.txt
for how to do this properly.

</formletter>


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