linux-kernel - Re: [PATCH] Don't apply for write lock on tasklist_lock if parent doesn't ptrace other processes

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Message-ID: <20100723173453.GA29831@redhat.com>
Date:	Fri, 23 Jul 2010 19:34:53 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Cc:	Roland McGrath <roland@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>, andi.kleen@...el.com,
	stable@...nel.org
Subject: Re: [PATCH] Don't apply for write lock on tasklist_lock if parent
	doesn't ptrace other processes

On 07/23, Zhang, Yanmin wrote:
>
> On Thu, 2010-07-22 at 11:05 +0200, Oleg Nesterov wrote:
> > I am not surpized perf blaims tasklist, but I am really surpized this patch
> > adds 10% improvement...
> I changed aim7 workfile to focus on fork/exec and other a couple of sub-cases.
> And this behavior is clear on 8-socket machines. 

Thanks...

> After applying my patch (although it's incorrect as there is a race with TRACEME),
> perf shows write_lock_irq in forget_original_parent consumes less than 40% cpu time on
> 8-socket machine.

Any chance you can test the patch I sent? It should have the same effect,
otherwise there is something interesting.

> Is it possible to optimize it to use finer locks instead of the global tasklist_lock?

Heh. We must optimize it. But it is not clear when ;)

Oleg.

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