linux-kernel - Re: [RFC,PATCH 0/2] do_wait() wakeup optimization

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Date:	Wed, 24 Jun 2009 17:41:51 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ratan Nalumasu <rnalumasu@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Roland McGrath <roland@...hat.com>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC,PATCH 0/2] do_wait() wakeup optimization

On 06/24, Ratan Nalumasu wrote:
>
> On Tue, Jun 23, 2009 at 7:30 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> > On 06/23, Ratan Nalumasu wrote:
> > >
> > > Yes, it is something we really need. The specific case I have (hundreds
> > of
> > > NTPL threads in a program, and each thread managing a child process), the
> > > CPU load is >99% with NTPL threads, near 0% with the patch
> >                                                    ^^^^^^^^^
> >
> > Thanks. Did you test this patch, or do you mean the previous one?
> >
>
> Sorry, I meant the previous patch. I realize that there are more steps to
> take before we get to a complete solution.

I think Roland has already showed us the necessary step.

I'd like to think a bit more before sending this patch, but any chance you
can test these 2 patches + "3/2" below?

Oleg.

--- WAIT/kernel/exit.c~	2009-06-22 18:55:08.000000000 +0200
+++ WAIT/kernel/exit.c	2009-06-24 17:32:03.000000000 +0200
@@ -1569,6 +1569,9 @@ static int child_wait_callback(wait_queu
 	if (!eligible_child(wo, p))
 		return 0;
 
+	if ((wo->wo_flags & __WNOTHREAD) && wait->private != p->parent)
+		return 0;
+
 	return default_wake_function(wait, mode, sync, key);
 }
 

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