Messages in this thread Patch in this message | | | From | Joel Fernandes <> | Date | Thu, 16 Nov 2017 13:53:58 -0800 | Subject | Re: [PATCH] sched/fair: Consider RT/IRQ pressure in capacity_spare_wake |
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Hi Vincent,
Thanks a lot for your reply, and sorry for the late reply. Actually I just started paternity leave so that's why the delay. My working hours and completely random at the moment :-)
On Fri, Nov 10, 2017 at 12:29 AM, Vincent Guittot <vincent.guittot@linaro.org> wrote: > On 9 November 2017 at 19:52, Joel Fernandes <joelaf@google.com> wrote: >> capacity_spare_wake in the slow path influences choice of idlest groups, >> as we search for groups with maximum spare capacity. In scenarios where >> RT pressure is high, a sub optimal group can be chosen and hurt >> performance of the task being woken up. >> >> Several tests with results are included below to show improvements with >> this change. >> >> 1) Hackbench on Pixel 2 Android device (4x4 ARM64 Octa core) > > "4x4 ARM64 Octa core" is confusing . At least for me, 4x4 means 16 cores :-)
Sure I'll fix it, I meant 4 big and 4 LITTLE CPUs :)
> >> ------------------------------------------------------------ >> Here we have RT activity running on big CPU cluster induced with rt-app, >> and running hackbench in parallel. The RT tasks are bound to 4 CPUs on >> the big cluster (cpu 4,5,6,7) and have 100ms periodicity with >> runtime=20ms sleep=80ms. >> >> Hackbench shows big benefit (30%) improvement when number of tasks is 8 >> and 32: Note: data is completion time in seconds (lower is better). >> Number of loops for 8 and 16 tasks is 50000, and for 32 tasks its 20000. >> +--------+-----+-------+-------------------+---------------------------+ >> | groups | fds | tasks | Without Patch | With Patch | >> +--------+-----+-------+---------+---------+-----------------+---------+ >> | | | | Mean | Stdev | Mean | Stdev | >> | | | +-------------------+-----------------+---------+ >> | 1 | 8 | 8 | 1.0534 | 0.13722 | 0.7293 (+30.7%) | 0.02653 | >> | 2 | 8 | 16 | 1.6219 | 0.16631 | 1.6391 (-1%) | 0.24001 | >> | 4 | 8 | 32 | 1.2538 | 0.13086 | 1.1080 (+11.6%) | 0.16201 | >> +--------+-----+-------+---------+---------+-----------------+---------+ > > Out of curiosity, do you know why you don't see any improvement for > 16 tasks but only for 8 and 32 tasks ?
Yes I'm not fully sure why 16 tasks didn't show that much improvement. I can try to trace it when I can get a chance. Generally for this test, with more number of tasks, the improvement is lesser. However you're right to point out that the improvement with 32 is > with 16 for this test.
[..] >> kernel/sched/fair.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 56f343b8e749..ba9609407cb9 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -5724,7 +5724,7 @@ static int cpu_util_wake(int cpu, struct task_struct *p); >> >> static unsigned long capacity_spare_wake(int cpu, struct task_struct *p) >> { >> - return capacity_orig_of(cpu) - cpu_util_wake(cpu, p); >> + return max_t(long, capacity_of(cpu) - cpu_util_wake(cpu, p), 0); > > Make sense > > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Thanks!
- Joel
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