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SubjectRe: power increase issue on light load
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On Thu, 2011-06-23 at 10:43 +0800, Alex,Shi wrote:
> commit c8b281161dfa4bb5d5be63fb036ce19347b88c63 causes light load
> benchmark use more than 10% system power on platform NHM-EP and laptop
> Thinkpad T410 etc. The benchmarks are specpower and bltk office.
>
> I tried to track this issue, but only find deep C sate time reduced
> much, about from 90% to 30~40%, the C0 or C1 state increase much on
> different machines.
>
> Powertop just hints RES interrupts has a bit more. but when I try "perf
> probe native_smp_send_reschedule". I didn't find much.
>
> I also checked the /proc/schedstat, just can sure the load_balance was
> called a bit more frequency. but pull_task() was called really rare.
>
>
> The following are the /proc/schedstat increased number in about 300' when do bltk-office.
> The getting command is here:
> #on a 16 LCPU system, with 3 level domain, 0,1,2, so all domain number
> is 48, the domain statistic number is 2 + 36, so fs=38,
>
> $cat /proc/schedstat > schedstat ; sleep x ; cat /proc/schedstat >>
> schedstat ; cat schedstat | grep domain | sed '49 i \\n' | awk -v fs=38
> 'BEGIN { RS=""; FS=" " } { if ( NR ==1) for (i=0; i<NF; i++)
> { value1[i]=$i ; } ; if ( NR ==2) for (i=0; i<NF; i++) { value2[i]=
> $i } } END {ORS=" "; for (i=0;i<NF;i++){ if (i%fs == 0) ll="\n"; else
> ll=""; print value2[i] - value1[i] ll }; print "\n" }'

/proc/schedstat is already a massive pain to interpret and then you go
and mangle things even more and expect me to try and understand that
crap? I don't think so, life is too short.

> BTW, the imbalance increasing is due to the SCALE increase about 1024.

> Any ideas of this?

What happens if you try something like the below. Increased imbalance
might lead to more load-balance action, which might lead to more task
migration/waking up of cpus etc.

If the below makes any difference, Nikhil's changes have a funny that
needs to be caught.

---
include/linux/sched.h | 6 ------
1 files changed, 0 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a837b20..84121d6 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -808,15 +808,9 @@ enum cpu_idle_type {
* when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the
* increased costs.
*/
-#if BITS_PER_LONG > 32
-# define SCHED_LOAD_RESOLUTION 10
-# define scale_load(w) ((w) << SCHED_LOAD_RESOLUTION)
-# define scale_load_down(w) ((w) >> SCHED_LOAD_RESOLUTION)
-#else
# define SCHED_LOAD_RESOLUTION 0
# define scale_load(w) (w)
# define scale_load_down(w) (w)
-#endif

#define SCHED_LOAD_SHIFT (10 + SCHED_LOAD_RESOLUTION)
#define SCHED_LOAD_SCALE (1L << SCHED_LOAD_SHIFT)


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