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: Tue, 8 Sep 2015 15:27:05 +0100 [thread overview]
Message-ID: <55EEF039.4040509@arm.com> (raw)
In-Reply-To: <CAKfTPtBNZL=VkuS3TVeQOptH+4aZR9aMyC2CfAxn8oSrmmFa2w@mail.gmail.com>
On 08/09/15 15:01, Vincent Guittot wrote:
> On 8 September 2015 at 14:50, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>> On 08/09/15 08:22, Vincent Guittot wrote:
>>> On 7 September 2015 at 20:54, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>>>> 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?
>>>
>>> It's both a unit and a SCALE/SHIFT problem, SCHED_LOAD_SHIFT and
>>> SCHED_CAPACITY_SHIFT are defined separately so we must be sure to
>>> scale the value in the right range. In the case of cpu_usage which
>>> returns sa->util_avg , it's the capacity range not the load range.
>>
>> Still don't understand why it's a unit problem. IMHO LOAD/UTIL and
>> CAPACITY have no unit.
>
> If you set 2 different values to SCHED_LOAD_SHIFT and
> SCHED_CAPACITY_SHIFT for test purpose, you will see that util_avg will
> not use the right range of value
>
> If we don't take into account freq and cpu invariance in a 1st step
>
> sa->util_sum is a load in the range [0..LOAD_AVG_MAX]. I say load
> because of the max value
>
> the current implementation of util_avg is
> sa->util_avg = (sa->util_sum << SCHED_LOAD_SHIFT) / LOAD_AVG_MAX
>
> so sa->util_avg is a load in the range [0..SCHED_LOAD_SCALE]
>
> the current implementation of get_cpu_usage is
> return (sa->util_avg * capacity_orig_of(cpu)) >> SCHED_LOAD_SHIFT
>
> so the usage has the same unit and range as capacity of the cpu and
> can be compared with another capacity value
>
> Your patchset returns directly sa->util_avg which is a load to compare
> it with capacity value
>
> So you have to convert sa->util_avg from load to capacity so if you have
> sa->util_avg = (sa->util_sum << SCHED_CAPACITY_SHIFT) / LOAD_AVG_MAX
>
> sa->util_avg is now a capacity with the same range as you cpu thanks
> to the cpu invariance factor that the patch 3 has added.
>
> the << SCHED_CAPACITY_SHIFT above can be optimized with the >>
> SCHED_CAPACITY_SHIFT included in
> sa->util_sum += scale(contrib, scale_cpu);
> as mentioned by Peter
>
> At now, SCHED_CAPACITY_SHIFT is set to 10 as well as SCHED_LOAD_SHIFT
> so using one instead of the other doesn't change the result but if
> it's no more the case, we need to take care of the range/unit that we
> use
No arguing here, I just called this a SHIFT/SCALE problem.
[...]
next prev parent reply other threads:[~2015-09-08 14:27 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
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 [this message]
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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