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 10:40:28 +0100
From:	"Kleen, Andi" <andi.kleen@...el.com>
To:	Oleg Nesterov <oleg@...hat.com>,
	"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>,
	"stable@...nel.org" <stable@...nel.org>
Subject: RE: [PATCH] Don't apply for write lock on tasklist_lock if parent
	doesn't ptrace other processes

> The only difference is that we are doing the function call +
> list_empty()
> under tasklist, just a few instructions compared to "do a lot more
> work"
> in forget_original_parent().
> 
> How this can make the 2% difference ? This looks like a noise to me,
> or do you think I missed something?

It could be a cache miss or something like that. Instructions are not
all the same cost. Only detailed profiling with different performance counters
could give you more information.

-Andi

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