linux-kernel - Re: [RFC] sched: make callers check lock contention for cond_resched

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Message-ID: <20120518072604.GG429@gmail.com>
Date:	Fri, 18 May 2012 09:26:05 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Takuya Yoshikawa <takuya.yoshikawa@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	kvm@...r.kernel.org, avi@...hat.com, mtosatti@...hat.com,
	yoshikawa.takuya@....ntt.co.jp
Subject: Re: [RFC] sched: make callers check lock contention for
 cond_resched_lock()


* Takuya Yoshikawa <takuya.yoshikawa@...il.com> wrote:

> Replaced Ingo's address with kernel.org one,
> 
> On Thu, 03 May 2012 17:47:30 +0200
> Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, 2012-05-03 at 22:00 +0900, Takuya Yoshikawa wrote:
> > > But as I could not see why spin_needbreak() was differently
> > > implemented
> > > depending on CONFIG_PREEMPT, I wanted to understand the meaning. 
> > 
> > Its been that way since before voluntary preemption was introduced, so
> > its possible Ingo simply missed that spot and nobody noticed until now.
> > 
> > Ingo, do you have any recollections from back when?
> 
> ping

I'm not sure we had a usable spin_is_contended() back then, nor 
was the !PREEMPT case in my mind really.

( The patch looks ugly though, in 99% of the lines it just does
  something that cond_resched_lock() itself could do. )

Thanks,

	Ingo
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