* [PATCH] sched/fair: refine maximum periods for decay_load
@ 2016-08-05 6:34 Leo Yan
2016-08-05 7:56 ` Vincent Guittot
0 siblings, 1 reply; 4+ messages in thread
From: Leo Yan @ 2016-08-05 6:34 UTC (permalink / raw)
To: Ingo Molnar, Peter Zijlstra, linux-kernel; +Cc: Leo Yan
In current code, decay_load() will consider to set load value to zero
after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.
Kernel can support maximum number of processes and threads to 2^29 and
set task with highest priority with nice=-20 (weight = 88761). So in
worst case, one CPU may have maximum load value is:
max_load = 2^29 * 88761 < 2^46
In theory after pass 46 periods we can ensure load value will be decayed
to zero. So this patch is to change maximum periods from 64 to 48.
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
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 e342159..55cb134 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)
if (!n)
return val;
- else if (unlikely(n > LOAD_AVG_PERIOD * 63))
+ else if (unlikely(n > LOAD_AVG_PERIOD * 47))
return 0;
/* after bounds checking we can collapse to 32-bit */
--
1.9.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] sched/fair: refine maximum periods for decay_load
2016-08-05 6:34 [PATCH] sched/fair: refine maximum periods for decay_load Leo Yan
@ 2016-08-05 7:56 ` Vincent Guittot
2016-08-05 8:17 ` Leo Yan
0 siblings, 1 reply; 4+ messages in thread
From: Vincent Guittot @ 2016-08-05 7:56 UTC (permalink / raw)
To: Leo Yan; +Cc: Ingo Molnar, Peter Zijlstra, linux-kernel
Hi Leo,
On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote:
>
> In current code, decay_load() will consider to set load value to zero
> after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.
>
> Kernel can support maximum number of processes and threads to 2^29 and
> set task with highest priority with nice=-20 (weight = 88761). So in
> worst case, one CPU may have maximum load value is:
>
> max_load = 2^29 * 88761 < 2^46
>
> In theory after pass 46 periods we can ensure load value will be decayed
> to zero. So this patch is to change maximum periods from 64 to 48.
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
> 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 e342159..55cb134 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)
>
> if (!n)
> return val;
> - else if (unlikely(n > LOAD_AVG_PERIOD * 63))
> + else if (unlikely(n > LOAD_AVG_PERIOD * 47))
In the equation above, you use 46 then you mentioned : "change maximum
periods from 64 to 48." and finally you use 47.
> return 0;
>
> /* after bounds checking we can collapse to 32-bit */
> --
> 1.9.1
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched/fair: refine maximum periods for decay_load
2016-08-05 7:56 ` Vincent Guittot
@ 2016-08-05 8:17 ` Leo Yan
2016-08-05 8:31 ` Vincent Guittot
0 siblings, 1 reply; 4+ messages in thread
From: Leo Yan @ 2016-08-05 8:17 UTC (permalink / raw)
To: Vincent Guittot; +Cc: Ingo Molnar, Peter Zijlstra, linux-kernel
Hi Vincent,
Thanks for review.
On Fri, Aug 05, 2016 at 09:56:46AM +0200, Vincent Guittot wrote:
> Hi Leo,
>
> On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote:
> >
> > In current code, decay_load() will consider to set load value to zero
> > after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.
> >
> > Kernel can support maximum number of processes and threads to 2^29 and
> > set task with highest priority with nice=-20 (weight = 88761). So in
> > worst case, one CPU may have maximum load value is:
> >
> > max_load = 2^29 * 88761 < 2^46
> >
> > In theory after pass 46 periods we can ensure load value will be decayed
> > to zero. So this patch is to change maximum periods from 64 to 48.
> >
> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
> > ---
> > 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 e342159..55cb134 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)
> >
> > if (!n)
> > return val;
> > - else if (unlikely(n > LOAD_AVG_PERIOD * 63))
> > + else if (unlikely(n > LOAD_AVG_PERIOD * 47))
>
> In the equation above, you use 46 then you mentioned : "change maximum
> periods from 64 to 48." and finally you use 47.
Sorry introduce confusion. I want to align to 16 so choose maximum
periods to 48, and due to condition is (n > LOAD_AVG_PERIOD * 47) so
it equeals to (n >= LOAD_AVG_PERIOD * 48).
Precisely I think the code should be:
else if (unlikely(n >= LOAD_AVG_PERIOD * 46))
Do you think this is okay?
> > return 0;
> >
> > /* after bounds checking we can collapse to 32-bit */
> > --
> > 1.9.1
> >
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] sched/fair: refine maximum periods for decay_load
2016-08-05 8:17 ` Leo Yan
@ 2016-08-05 8:31 ` Vincent Guittot
0 siblings, 0 replies; 4+ messages in thread
From: Vincent Guittot @ 2016-08-05 8:31 UTC (permalink / raw)
To: Leo Yan; +Cc: Ingo Molnar, Peter Zijlstra, linux-kernel
On 5 August 2016 at 10:17, Leo Yan <leo.yan@linaro.org> wrote:
> Hi Vincent,
>
> Thanks for review.
>
> On Fri, Aug 05, 2016 at 09:56:46AM +0200, Vincent Guittot wrote:
>> Hi Leo,
>>
>> On 5 August 2016 at 08:34, Leo Yan <leo.yan@linaro.org> wrote:
>> >
>> > In current code, decay_load() will consider to set load value to zero
>> > after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.
>> >
>> > Kernel can support maximum number of processes and threads to 2^29 and
>> > set task with highest priority with nice=-20 (weight = 88761). So in
>> > worst case, one CPU may have maximum load value is:
>> >
>> > max_load = 2^29 * 88761 < 2^46
>> >
>> > In theory after pass 46 periods we can ensure load value will be decayed
>> > to zero. So this patch is to change maximum periods from 64 to 48.
>> >
>> > Signed-off-by: Leo Yan <leo.yan@linaro.org>
>> > ---
>> > 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 e342159..55cb134 100644
>> > --- a/kernel/sched/fair.c
>> > +++ b/kernel/sched/fair.c
>> > @@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)
>> >
>> > if (!n)
>> > return val;
>> > - else if (unlikely(n > LOAD_AVG_PERIOD * 63))
>> > + else if (unlikely(n > LOAD_AVG_PERIOD * 47))
>>
>> In the equation above, you use 46 then you mentioned : "change maximum
>> periods from 64 to 48." and finally you use 47.
>
> Sorry introduce confusion. I want to align to 16 so choose maximum
> periods to 48, and due to condition is (n > LOAD_AVG_PERIOD * 47) so
> it equeals to (n >= LOAD_AVG_PERIOD * 48).
>
> Precisely I think the code should be:
> else if (unlikely(n >= LOAD_AVG_PERIOD * 46))
>
> Do you think this is okay?
yes, this looks okay
>
>> > return 0;
>> >
>> > /* after bounds checking we can collapse to 32-bit */
>> > --
>> > 1.9.1
>> >
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2016-08-05 8:31 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2016-08-05 6:34 [PATCH] sched/fair: refine maximum periods for decay_load Leo Yan
2016-08-05 7:56 ` Vincent Guittot
2016-08-05 8:17 ` Leo Yan
2016-08-05 8:31 ` Vincent Guittot
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.