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

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Date:	Mon, 23 Mar 2009 17:17:04 +0100
From:	Miklos Szeredi <miklos@...redi.hu>
To:	mingo@...e.hu
CC:	miklos@...redi.hu, linux-kernel@...r.kernel.org, oleg@...hat.com,
	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

On Mon, 23 Mar 2009, Ingo Molnar wrote:
> * Miklos Szeredi <miklos@...redi.hu> wrote:
> 
> > This one incorporates comments from Oleg and Ingo.  Please apply 
> > to 2.6.29 and 2.6.2[78]-stable trees.
> 
> The fix first needs to go upstream. 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.

Just the opposite.  With my patch a UML image boots in 17 seconnds,
with your patch it boots in 33 seconds.  Without either patch it boots
in about 5 minutes.

Thanks,
Miklos

> 
> 	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();
>  			continue;
>  		}
>  
> 
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