From: Morten Rasmussen <morten.rasmussen@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.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: Wed, 9 Sep 2015 12:13:10 +0100 [thread overview]
Message-ID: <20150909111309.GD27098@e105550-lin.cambridge.arm.com> (raw)
In-Reply-To: <20150909094305.GO3644@twins.programming.kicks-ass.net>
On Wed, Sep 09, 2015 at 11:43:05AM +0200, Peter Zijlstra wrote:
> On Tue, Sep 08, 2015 at 05:53:31PM +0100, Morten Rasmussen wrote:
> > 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:
> > > But if we apply the scaling to the weight instead of time, we would only
> > > have to apply it once and not three times like it is now? So maybe we
> > > can end up with almost the same number of multiplications.
> > >
> > > We might be loosing bits for low priority task running on cpus at a low
> > > frequency though.
> >
> > Something like the below. We should be saving one multiplication.
>
> > @@ -2577,8 +2575,13 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
> > return 0;
> > sa->last_update_time = now;
> >
> > - scale_freq = arch_scale_freq_capacity(NULL, cpu);
> > - scale_cpu = arch_scale_cpu_capacity(NULL, cpu);
> > + if (weight || running)
> > + scale_freq = arch_scale_freq_capacity(NULL, cpu);
> > + if (weight)
> > + scaled_weight = weight * scale_freq >> SCHED_CAPACITY_SHIFT;
> > + if (running)
> > + scale_freq_cpu = scale_freq * arch_scale_cpu_capacity(NULL, cpu)
> > + >> SCHED_CAPACITY_SHIFT;
> >
> > /* delta_w is the amount already accumulated against our next period */
> > delta_w = sa->period_contrib;
> > @@ -2594,16 +2597,15 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa,
> > * period and accrue it.
> > */
> > delta_w = 1024 - delta_w;
> > - scaled_delta_w = cap_scale(delta_w, scale_freq);
> > if (weight) {
> > - sa->load_sum += weight * scaled_delta_w;
> > + sa->load_sum += scaled_weight * delta_w;
> > if (cfs_rq) {
> > cfs_rq->runnable_load_sum +=
> > - weight * scaled_delta_w;
> > + scaled_weight * delta_w;
> > }
> > }
> > if (running)
> > - sa->util_sum += scaled_delta_w * scale_cpu;
> > + sa->util_sum += delta_w * scale_freq_cpu;
> >
> > delta -= delta_w;
> >
>
> Sadly that makes the code worse; I get 14 mul instructions where
> previously I had 11.
>
> What happens is that GCC gets confused and cannot constant propagate the
> new variables, so what used to be shifts now end up being actual
> multiplications.
>
> With this, I get back to 11. Can you see what happens on ARM where you
> have both functions defined to non constants?
We repeated the experiment on arm and arm64 but still with functions
defined to constant to compare with your results. The mul instruction
count seems to be somewhat compiler version dependent, but consistently
show no effect of the patch:
arm before after
gcc4.9 12 12
gcc4.8 10 10
arm64 before after
gcc4.9 11 11
I will get numbers with the arch-functions implemented as well and do
hackbench runs to see what happens in terms of performance.
next prev parent reply other threads:[~2015-09-09 11:09 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 [this message]
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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