linux-kernel - Re: sched_yield: delete sysctl_sched_compat

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Message-ID: <20071203101702.GB30050@elte.hu>
Date:	Mon, 3 Dec 2007 11:17:02 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Nick Piggin <nickpiggin@...oo.com.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched_yield: delete sysctl_sched_compat_yield

* Zhang, Yanmin <yanmin_zhang@...ux.intel.com> wrote:

> > as far as desktop apps such as firefox goes, the exact opposite is 
> > true. We had two choices basically: either a "more agressive" yield 
> > than before or a "less agressive" yield. Desktop apps were reported 
> > to hurt from a "more agressive" yield (firefox for example gets some 
> > pretty bad delays),
>
> Why not to change source codes of firefox? [...]

because we care a heck of a lot more about a widely used open-source 
package's default "user experience" than we care about closed-source 
volanomark scores...

do you realize the absurdity of that suggestion: in essence we'd punish 
firefox _because it is open-source and can be changed_. So basically 
firefox would get a more preferential treatment if it was closed-source 
and could not be changed? That's totally backwards.

> If the sched_compat_yield=0, the sys_sched_yield almost does nothing 
> but returns, so firefox could just do not call sched_yield. I assume 
> 'sched_compat_yield=0' ~ no_call_to_sched_yield.
> 
> It's easier to delete calls to sched_yield in applications than to 
> tune calls to sched_yield.

We are not at all worried about punishing silly benchmark behavior - and 
volanomark's call to Thread.yield (if that's indeed what is happening - 
could you try to trace it to make sure?) is outright silly. There are 
other chatroom benchmarks such as hackbench.c and hackbench_pth.c that i 
test frequently, and they are not affected by any yield details. (and 
even then it's still taken with a grain of salt - remember dbench)

	Ingo
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