From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Steve Muckle <steve.muckle@linaro.org>,
Morten Rasmussen <Morten.Rasmussen@arm.com>,
"peterz@infradead.org" <peterz@infradead.org>,
"mingo@redhat.com" <mingo@redhat.com>,
"daniel.lezcano@linaro.org" <daniel.lezcano@linaro.org>,
"yuyang.du@intel.com" <yuyang.du@intel.com>,
"mturquette@baylibre.com" <mturquette@baylibre.com>,
"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
Juri Lelli <Juri.Lelli@arm.com>,
"sgurrappadi@nvidia.com" <sgurrappadi@nvidia.com>,
"pang.xunlei@zte.com.cn" <pang.xunlei@zte.com.cn>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig
Date: Mon, 7 Sep 2015 19:54:18 +0100 [thread overview]
Message-ID: <55EDDD5A.70904@arm.com> (raw)
In-Reply-To: <CAKfTPtBmgc=7JMRcTL9VYdHxb7qgXBDFc62rb-jnSVCePwJNsg@mail.gmail.com>
On 07/09/15 17:21, Vincent Guittot wrote:
> On 7 September 2015 at 17:37, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>> On 04/09/15 00:51, Steve Muckle wrote:
>>> Hi Morten, Dietmar,
>>>
>>> On 08/14/2015 09:23 AM, Morten Rasmussen wrote:
>>> ...
>>>> + * cfs_rq.avg.util_avg is the sum of running time of runnable tasks plus the
>>>> + * recent utilization of currently non-runnable tasks on a CPU. It represents
>>>> + * the amount of utilization of a CPU in the range [0..capacity_orig] where
>>>
>>> I see util_sum is scaled by SCHED_LOAD_SHIFT at the end of
>>> __update_load_avg(). If there is now an assumption that util_avg may be
>>> used directly as a capacity value, should it be changed to
>>> SCHED_CAPACITY_SHIFT? These are equal right now, not sure if they will
>>> always be or if they can be combined.
>>
>> You're referring to the code line
>>
>> 2647 sa->util_avg = (sa->util_sum << SCHED_LOAD_SHIFT) / LOAD_AVG_MAX;
>>
>> in __update_load_avg()?
>>
>> Here we actually scale by 'SCHED_LOAD_SCALE/LOAD_AVG_MAX' so both values are
>> load related.
>
> I agree with Steve that there is an issue from a unit point of view
>
> sa->util_sum and LOAD_AVG_MAX have the same unit so sa->util_avg is a
> load because of << SCHED_LOAD_SHIFT)
>
> Before this patch , the translation from load to capacity unit was
> done in get_cpu_usage with "* capacity) >> SCHED_LOAD_SHIFT"
>
> So you still have to change the unit from load to capacity with a "/
> SCHED_LOAD_SCALE * SCHED_CAPACITY_SCALE" somewhere.
>
> sa->util_avg = ((sa->util_sum << SCHED_LOAD_SHIFT) /SCHED_LOAD_SCALE *
> SCHED_CAPACITY_SCALE / LOAD_AVG_MAX = (sa->util_sum <<
> SCHED_CAPACITY_SHIFT) / LOAD_AVG_MAX;
I see the point but IMHO this will only be necessary if the SCHED_LOAD_RESOLUTION
stuff gets re-enabled again.
It's not really about utilization or capacity units but rather about using the same
SCALE/SHIFT values for both sides, right?
I always thought that scale_load_down() takes care of that.
So shouldn't:
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 3445d2fb38f4..b80f799aface 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2644,7 +2644,7 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
cfs_rq->runnable_load_avg =
div_u64(cfs_rq->runnable_load_sum, LOAD_AVG_MAX);
}
- sa->util_avg = (sa->util_sum << SCHED_LOAD_SHIFT) / LOAD_AVG_MAX;
+ sa->util_avg = (sa->util_sum * scale_load_down(SCHED_LOAD_SCALE)) / LOAD_AVG_MAX;
}
return decayed;
fix that issue in case SCHED_LOAD_RESOLUTION != 0 ?
I would vote for removing this SCHED_LOAD_RESOLUTION thing completely so that we can
assume that load/util and capacity are always using 1024/10.
Cheers,
-- Dietmar
>
>
> Regards,
> Vincent
>
>
>>
>> LOAD (UTIL) and CAPACITY have the same SCALE and SHIFT values because
>> SCHED_LOAD_RESOLUTION is always defined to 0. scale_load() and
>> scale_load_down() are also NOPs so this area is probably
>> worth a separate clean-up.
>> Beyond that, I'm not sure if the current functionality is
>> broken if we use different SCALE and SHIFT values for LOAD and CAPACITY?
>>
[...]
next prev parent reply other threads:[~2015-09-07 18:54 UTC|newest]
Thread overview: 97+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-14 16:23 [PATCH 0/6] sched/fair: Compute capacity invariant load/utilization tracking Morten Rasmussen
2015-08-14 16:23 ` [PATCH 1/6] sched/fair: Make load tracking frequency scale-invariant Morten Rasmussen
2015-09-13 11:03 ` [tip:sched/core] " tip-bot for Dietmar Eggemann
2015-08-14 16:23 ` [PATCH 2/6] sched/fair: Convert arch_scale_cpu_capacity() from weak function to #define Morten Rasmussen
2015-09-02 9:31 ` Vincent Guittot
2015-09-02 12:41 ` Vincent Guittot
2015-09-03 19:58 ` Dietmar Eggemann
2015-09-04 7:26 ` Vincent Guittot
2015-09-07 13:25 ` Dietmar Eggemann
2015-09-11 13:21 ` Dietmar Eggemann
2015-09-11 14:45 ` Vincent Guittot
2015-09-13 11:03 ` [tip:sched/core] " tip-bot for Morten Rasmussen
2015-08-14 16:23 ` [PATCH 3/6] sched/fair: Make utilization tracking cpu scale-invariant Morten Rasmussen
2015-08-14 23:04 ` Dietmar Eggemann
2015-09-04 7:52 ` Vincent Guittot
2015-09-13 11:04 ` [tip:sched/core] sched/fair: Make utilization tracking CPU scale-invariant tip-bot for Dietmar Eggemann
2015-08-14 16:23 ` [PATCH 4/6] sched/fair: Name utilization related data and functions consistently Morten Rasmussen
2015-09-04 9:08 ` Vincent Guittot
2015-09-11 16:35 ` Dietmar Eggemann
2015-09-13 11:04 ` [tip:sched/core] " tip-bot for Dietmar Eggemann
2015-08-14 16:23 ` [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig Morten Rasmussen
2015-09-03 23:51 ` Steve Muckle
2015-09-07 15:37 ` Dietmar Eggemann
2015-09-07 16:21 ` Vincent Guittot
2015-09-07 18:54 ` Dietmar Eggemann [this message]
2015-09-07 19:47 ` Peter Zijlstra
2015-09-08 12:47 ` Dietmar Eggemann
2015-09-08 7:22 ` Vincent Guittot
2015-09-08 12:26 ` Peter Zijlstra
2015-09-08 12:52 ` Peter Zijlstra
2015-09-08 14:06 ` Vincent Guittot
2015-09-08 14:35 ` Morten Rasmussen
2015-09-08 14:40 ` Vincent Guittot
2015-09-08 14:31 ` Morten Rasmussen
2015-09-08 15:33 ` Peter Zijlstra
2015-09-09 22:23 ` bsegall
2015-09-10 11:06 ` Morten Rasmussen
2015-09-10 11:11 ` Vincent Guittot
2015-09-10 12:10 ` Morten Rasmussen
2015-09-11 0:50 ` Yuyang Du
2015-09-10 17:23 ` bsegall
2015-09-08 16:53 ` Morten Rasmussen
2015-09-09 9:43 ` Peter Zijlstra
2015-09-09 9:45 ` Peter Zijlstra
2015-09-09 11:13 ` Morten Rasmussen
2015-09-11 17:22 ` Morten Rasmussen
2015-09-17 9:51 ` Peter Zijlstra
2015-09-17 10:38 ` Peter Zijlstra
2015-09-21 1:16 ` Yuyang Du
2015-09-21 17:30 ` bsegall
2015-09-21 23:39 ` Yuyang Du
2015-09-22 17:18 ` bsegall
2015-09-22 23:22 ` Yuyang Du
2015-09-23 16:54 ` bsegall
2015-09-24 0:22 ` Yuyang Du
2015-09-30 12:52 ` Peter Zijlstra
2015-09-11 7:46 ` Leo Yan
2015-09-11 10:02 ` Morten Rasmussen
2015-09-11 14:11 ` Leo Yan
2015-09-09 19:07 ` Yuyang Du
2015-09-10 10:06 ` Peter Zijlstra
2015-09-08 13:39 ` Vincent Guittot
2015-09-08 14:10 ` Peter Zijlstra
2015-09-08 15:17 ` Vincent Guittot
2015-09-08 12:50 ` Dietmar Eggemann
2015-09-08 14:01 ` Vincent Guittot
2015-09-08 14:27 ` Dietmar Eggemann
2015-09-09 20:15 ` Yuyang Du
2015-09-10 10:07 ` Peter Zijlstra
2015-09-11 0:28 ` Yuyang Du
2015-09-11 10:31 ` Morten Rasmussen
2015-09-11 17:05 ` bsegall
2015-09-11 18:24 ` Yuyang Du
2015-09-14 17:36 ` bsegall
2015-09-14 12:56 ` Morten Rasmussen
2015-09-14 17:34 ` bsegall
2015-09-14 22:56 ` Yuyang Du
2015-09-15 17:11 ` bsegall
2015-09-15 18:39 ` Yuyang Du
2015-09-16 17:06 ` bsegall
2015-09-17 2:31 ` Yuyang Du
2015-09-15 8:43 ` Morten Rasmussen
2015-09-16 15:36 ` Peter Zijlstra
2015-09-08 11:44 ` Peter Zijlstra
2015-09-13 11:04 ` [tip:sched/core] " tip-bot for Dietmar Eggemann
2015-08-14 16:23 ` [PATCH 6/6] sched/fair: Initialize task load and utilization before placing task on rq Morten Rasmussen
2015-09-13 11:05 ` [tip:sched/core] " tip-bot for Morten Rasmussen
2015-08-16 20:46 ` [PATCH 0/6] sched/fair: Compute capacity invariant load/utilization tracking Peter Zijlstra
2015-08-17 11:29 ` Morten Rasmussen
2015-08-17 11:48 ` Peter Zijlstra
2015-08-31 9:24 ` Peter Zijlstra
2015-09-02 9:51 ` Dietmar Eggemann
2015-09-07 12:42 ` Peter Zijlstra
2015-09-07 13:21 ` Peter Zijlstra
2015-09-07 13:23 ` Peter Zijlstra
2015-09-07 14:44 ` Dietmar Eggemann
2015-09-13 11:06 ` [tip:sched/core] sched/fair: Defer calling scaling functions tip-bot for Dietmar Eggemann
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