From: Vincent Guittot <vincent.guittot@linaro.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
Cc: Benjamin Segall <bsegall@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steve Muckle <steve.muckle@linaro.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: Thu, 10 Sep 2015 13:11:01 +0200 [thread overview]
Message-ID: <CAKfTPtCKAAhU4hbkRG2-m1n=koYts4t6ozmHj=P+6GTRNkkiuQ@mail.gmail.com> (raw)
In-Reply-To: <20150910110638.GE27098@e105550-lin.cambridge.arm.com>
On 10 September 2015 at 13:06, Morten Rasmussen
<morten.rasmussen@arm.com> wrote:
> On Wed, Sep 09, 2015 at 03:23:43PM -0700, bsegall@google.com wrote:
>> Peter Zijlstra <peterz@infradead.org> writes:
>>
>> > On Tue, Sep 08, 2015 at 03:31:58PM +0100, Morten Rasmussen wrote:
>> >> On Tue, Sep 08, 2015 at 02:52:05PM +0200, Peter Zijlstra wrote:
>> >> > > Tricky that, LOAD_AVG_MAX very much relies on the unit being 1<<10.
>> >>
>> >> I don't get why LOAD_AVG_MAX relies on the util_avg shifting being
>> >> 1<<10, it is just the sum of the geometric series and the upper bound of
>> >> util_sum?
>> >
>> > It needs a 1024, it might just have been the 1024 ns we use a period
>> > instead of the scale unit though.
>> >
>> > The LOAD_AVG_MAX is the number where adding a next element to the series
>> > doesn't change the result anymore, so scaling it up will allow more
>> > significant elements to the series before we bottom out, which is the _N
>> > thing.
>> >
>>
>> Yes, as the comments say, the 1024ns unit is arbitrary (and is an
>> average of not-quite-microseconds instead of just nanoseconds to allow
>> more bits to load.weight when we multiply load.weight by this number).
>> In fact there are two arbitrary 1024 units here, which are technically
>> unrelated and are both unrelated to SCHED_LOAD_RESOLUTION/etc - we
>> operate on units of almost-microseconds and we also do decays every
>> almost-millisecond.
>>
>> There appears to be a bunch of confusion in the current code around
>> util_sum/util_avg which appears to using SCHED_LOAD_SCALE
>> for a fixed-point percentage or something, which is at least reasonable,
>> but is initializing it as scale_load_down(SCHED_LOAD_SCALE), which
>> results in either initializing as 100% or .1% depending on RESOLUTION.
>> This'll get clobbered on first update, but if it needs to be
>> initialized, it should either get initialized to something sane or at
>> least consistent.
>
> This is what I thought too. The whole geometric series math is completely
> independent of the scale used for priority in load_avg and the fixed
> point shifting used for util_avg.
>
>> load_sum/load_avg appear to be scale_load_down()ed properly, and appear
>> to be used as such at a quick glance.
>
> I don't think shifting by SCHED_LOAD_SHIFT in __update_load_avg() is
> right:
>
> sa->util_avg = (sa->util_sum << SCHED_LOAD_SHIFT) / LOAD_AVG_MAX;
>
> util_avg is initialized to low resolution (>> SCHED_LOAD_RESOLUTION):
>
> sa->util_avg = scale_load_down(SCHED_LOAD_SCALE);
>
> so it appear to be intended to be using low resolution like load_avg
> (weight is scaled down before it is passed into __update_load_avg()),
> but util_avg is shifted up to high resolution. It should be:
>
> sa->util_avg = (sa->util_sum << (SCHED_LOAD_SHIFT -
> SCHED_LOAD_SHIFT)) / LOAD_AVG_MAX;
you probably mean (SCHED_LOAD_SHIFT - SCHED_LOAD_RESOLUTION)
The goal of this patchset is to be able to scale util_avg in the range
of cpu capacity so why don't we directly initialize it with
sa->util_avg = SCHED_CAPACITY_SCALE;
and then use
sa->util_avg = (sa->util_sum << SCHED_CAPACITY_SHIFT) / LOAD_AVG_MAX;
so we don't have to take care of high and low load resolution
Regards,
>
> to be consistent.
next prev parent reply other threads:[~2015-09-10 11:11 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 [this message]
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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