On 16 November 2017 at 22:53, Joel Fernandes joelaf@google.com wrote:
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
Congratulations !
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.
- 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.
Yes. This is just to make sure that there no unexpected side effect
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