From: Juri Lelli <juri.lelli@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Joe Perches <joe@perches.com>, Yuyang Du <yuyang.du@intel.com>,
mingo@kernel.org, linux-kernel@vger.kernel.org,
bsegall@google.com, pjt@google.com, morten.rasmussen@arm.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com
Subject: Re: [PATCH] sched/fair: Optimize sum computation with a lookup table
Date: Fri, 8 Apr 2016 09:22:45 -0700 [thread overview]
Message-ID: <20160408162245.GB11241@pablo> (raw)
In-Reply-To: <20160408105423.GN3448@twins.programming.kicks-ass.net>
Hi,
On 08/04/16 12:54, Peter Zijlstra wrote:
> On Fri, Apr 08, 2016 at 03:31:41AM -0700, Joe Perches wrote:
> > On Fri, 2016-04-08 at 10:07 +0800, Yuyang Du wrote:
> > > __compute_runnable_contrib() uses a loop to compute sum, whereas a
> > > table lookup can do it faster in a constant time.
> >
> > Perhaps this becomes rather fragile code overly dependent on the
> > current #define values of LOAD_AVG_MAX_N and LOAD_AVG_PERIOD.
>
> Too late for that, these tables already heavily depend on these values.
>
> Commit 5b51f2f80b3b ("sched: Make __update_entity_runnable_avg() fast"),
> which introduced these tables, includes a program to re-compute the
> values if we ever need to change them.
>
> It might maybe make sense for Yuyang to update that program to also
> compute this new table and include the whole new program in the
> Changelog of this patch.
>
+1 on this. That program turns out to be really useful if one needs to
recompute tables.
Best,
- Juri
next prev parent reply other threads:[~2016-04-08 16:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-08 2:07 [PATCH] sched/fair: Optimize sum computation with a lookup table Yuyang Du
2016-04-08 10:31 ` Joe Perches
2016-04-08 10:54 ` Peter Zijlstra
2016-04-08 16:22 ` Juri Lelli [this message]
2016-04-08 10:44 ` Peter Zijlstra
2016-04-08 10:45 ` Peter Zijlstra
2016-04-08 11:30 ` Morten Rasmussen
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