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: <alpine.DEB.2.00.1007151250430.29400@chino.kir.corp.google.com>
Date:	Thu, 15 Jul 2010 12:53:43 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, andi.kleen@...el.com
Subject: Re: [PATCH] Don't apply for write lock on tasklist_lock if parent
 doesn't ptrace other processes

On Thu, 15 Jul 2010, Zhang, Yanmin wrote:

> We run some sub-cases (fork, exec, pipe, tcp, udp) of aim7 on 8-socket machine.
> Perf shows write_lock_irq(&tasklist_lock) consumes more than 50% cpu time.
> 
> One hot caller is exit_ptrace. If the exiting process doesn't ptrace other
> processes, kernel needn't apply for the write lock on tasklist_lock.
> 
> With below patch against kernel 2.6.35-rc5, we get more than 10% result improvement.
> 
> Signed-off-by: Zhang Yanmin <yanmin_zhang@...ux.intel.com>

Acked-by: David Rientjes <rientjes@...gle.com>

We're guarded against ptrace_attach() because tracer->exit_state is 
non-zero at this point in the exit path.
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