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

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Message-ID: <20090323155303.GA5528@redhat.com>
Date:	Mon, 23 Mar 2009 16:53:03 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
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

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?

Oleg.

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