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

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Date:	Mon, 26 Jul 2010 13:05:31 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	Oleg Nesterov <oleg@...hat.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 Fri, 2010-07-23 at 19:34 +0200, Oleg Nesterov wrote:
> 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.
1) with my patch, we got about 13% improvement;
2) With your patch, we got about 11% improvement;

Performance is very sensitive to spinlock contention on large machines.
 
> 
> > 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 ;)
Thanks. It's better to remove the big lock.


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