linux-kernel - Re: [PATCH][resubmit] x86: enable preemption in delay

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Message-Id: <200806182242.49245.nickpiggin@yahoo.com.au>
Date:	Wed, 18 Jun 2008 22:42:48 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	"Gregory Haskins" <ghaskins@...ell.com>
Cc:	"Peter Zijlstra" <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Andi Kleen" <andi-suse@...stfloor.org>,
	"Clark Williams" <clark.williams@...il.com>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Marin Mitov" <mitov@...p.bas.bg>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>, akpm@...l.org,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"linux-rt-users" <linux-rt-users@...r.kernel.org>
Subject: Re: [PATCH][resubmit] x86: enable preemption in delay

On Wednesday 18 June 2008 22:25, Gregory Haskins wrote:
> >>> On Wed, Jun 18, 2008 at  8:16 AM, in message

> > Yeah - migrate_disable() has been proposed several times. The reason I
> > don't like it is that is creates scheduling artefacts like latencies by
> > not being able to load-balance (and thereby complicates all that, and
> > you know we don't need more complication there).
>
> True, and good point.  But this concept would certainly be useful to avoid
> the heavyweight (w.r.t. latency) preempt-disable() in quite a few different
> areas, so if we can make it work with reasonable visibility, it might be
> nice to have.

It just seems like pretty worthless bloat to me.

There are _some_ cases where it can be used, but nobody has been
able to come up with compelling uses really. I don't think this
case is helped very much either because the logic in there using
preempt-disable is fine, isn't it?

Except that it should also have a cond_resched in it. Seems like
an ideal place to put cond_resched because it is not a fastpath.
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