From: Andi Kleen <andi@firstfloor.org>
To: "Robert P. J. Day" <rpjday@crashcourse.ca>
Cc: Andi Kleen <andi@firstfloor.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] RWSEM: Rewrite rwsem.c and rwsem-spinlock.c more simply.
Date: Tue, 25 Mar 2008 13:36:33 +0100 [thread overview]
Message-ID: <20080325123633.GL2170@one.firstfloor.org> (raw)
In-Reply-To: <alpine.LFD.1.00.0803250813190.19386@localhost.localdomain>
> i'm not sure what this means -- which of the transformations in that
> patch is considered unsafe? here's a typical simplification:
It is not unsafe, just generates slight worse code.
current is inline assembler and the compiler doesn't know that it could
cache it in a register because it is not marked pure
for various reasons. That is why current is often cached explicitely
in a local variable to tell the compiler that.
Before you run off and do that everywhere: it is also not a large
win, just a small one unless current is used very often.
-Andi
next prev parent reply other threads:[~2008-03-25 12:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-03-25 11:02 Robert P. J. Day
2008-03-25 12:08 ` Andi Kleen
2008-03-25 12:27 ` Robert P. J. Day
2008-03-25 12:36 ` Andi Kleen [this message]
2008-03-25 12:42 ` Robert P. J. Day
2008-03-25 19:14 ` Andrew Morton
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