From: Peter Zijlstra <peterz@infradead.org>
To: Morten Rasmussen <morten.rasmussen@arm.com>
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 11:43:05 +0200 [thread overview]
Message-ID: <20150909094305.GO3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150908165331.GC27098@e105550-lin.cambridge.arm.com>
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?
---
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2551,10 +2551,10 @@ static __always_inline int
__update_load_avg(u64 now, int cpu, struct sched_avg *sa,
unsigned long weight, int running, struct cfs_rq *cfs_rq)
{
+ unsigned long scaled_weight, scale_freq, scale_freq_cpu;
+ unsigned int delta_w, decayed = 0;
u64 delta, periods;
u32 contrib;
- unsigned int delta_w, decayed = 0;
- unsigned long scaled_weight = 0, scale_freq, scale_freq_cpu = 0;
delta = now - sa->last_update_time;
/*
@@ -2575,13 +2575,10 @@ __update_load_avg(u64 now, int cpu, stru
return 0;
sa->last_update_time = now;
- 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;
+ scale_freq = arch_scale_freq_capacity(NULL, cpu);
+
+ scaled_weight = weight * scale_freq >> SCHED_CAPACITY_SHIFT;
+ 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;
next prev parent reply other threads:[~2015-09-09 9:43 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 [this message]
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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