linux-kernel - Re: [patch] fix ptrace slowness

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Message-ID: <20090323161358.GB24940@elte.hu>
Date:	Mon, 23 Mar 2009 17:13:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-kernel@...r.kernel.org,
	peterz@...radead.org, roland@...hat.com, efault@....de,
	rjw@...k.pl, jdike@...toit.com,
	user-mode-linux-devel@...ts.sourceforge.net,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	stable@...nel.org
Subject: Re: [patch] fix ptrace slowness


* Oleg Nesterov <oleg@...hat.com> wrote:

> On 03/23, Ingo Molnar wrote:
> >
> > There's an alternative patch
> > below. Would you mind to give it a test? Chances are that it will
> > make UML even faster than your fix.
> >
> > 	Ingo
> >
> > diff --git a/kernel/sched.c b/kernel/sched.c
> > index 3e827b8..2d60f23 100644
> > --- a/kernel/sched.c
> > +++ b/kernel/sched.c
> > @@ -2119,7 +2119,8 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
> >  		 * yield - it could be a while.
> >  		 */
> >  		if (unlikely(on_rq)) {
> > -			schedule_timeout_uninterruptible(1);
> > +			cpu_relax();
> > +			cond_resched();
> 
> What if the caller is a realtime task? We can spin "forever", no?

hm, yes. I sure should have noticed _that_ ;-)

	Ingo
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