linux-kernel - Re: sched_yield: delete sysctl_sched_compat

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Date:	Mon, 3 Dec 2007 21:15:43 +1100
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	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

On Monday 03 December 2007 20:57, Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@...oo.com.au> 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), so we defaulted to the less agressive method.
> > > (and we defaulted to that in v2.6.23 already)
> >
> > Yeah, I doubt the 2.6.23 scheduler will be usable for distros
> > though...
>
> ... which is a pretty gross exaggeration belied by distros already
> running v2.6.23. Sure, "enterprise" distros might not run .23 (or .22 or

Yeah, that's what I mean of course. And it's because of the performance
and immediate upstream divergence issues with 2.6.23. Specifically I'm
talking about the scheduler: they may run a base 2.6.23, but it would
likely have most or all subsequent scheduler patches.


> > I was just talking about the default because I didn't know the reason
> > for the way it was set -- now that I do, we should talk about trying
> > to improve the actual code so we don't need 2 defaults.
>
> I've got the patch below queued up: it uses the more agressive yield
> implementation for SCHED_BATCH tasks. SCHED_BATCH is a natural
> differentiator, it's a "I dont care about latency, it's all about
> throughput for me" signal from the application.

First and foremost, do you realize that I'm talking about existing
userspace working well on future kernels right? (ie. backwards
compatibility).


> But first and foremost, do you realize that there will be no easy
> solutions to this topic, that it's not just about 'flipping a default'?

Of course ;) I already answered that in the email that you're replying
to:

> > I was just talking about the default because I didn't know the reason
> > for the way it was set -- now that I do, we should talk about trying
> > to improve the actual code so we don't need 2 defaults.

Anyway, I'd hope it can actually be improved and even the sysctl
removed completely.
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