From: Ingo Molnar <mingo@redhat.com>
To: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Ingo Molnar <mingo@elte.hu>, Hugh Dickins <hugh@veritas.com>,
Linus Torvalds <torvalds@osdl.org>,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [patch] fix i386 mutex fastpath on FRAME_POINTER && !DEBUG_MUTEXES
Date: Wed, 11 Jan 2006 05:13:00 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.58.0601110511590.24014@devserv.devel.redhat.com> (raw)
In-Reply-To: <200601110327_MC3-1-B5A3-6E0E@compuserve.com>
On Wed, 11 Jan 2006, Chuck Ebbert wrote:
> In-Reply-To: <20060110210744.GA8850@elte.hu>
>
> On Tue, 10 Jan 2006 at 22:07:44 +0100, Ingo Molnar wrote:
>
> > --- linux.orig/include/asm-i386/mutex.h
> > +++ linux/include/asm-i386/mutex.h
> > @@ -28,7 +28,13 @@ do { \
> > \
> > __asm__ __volatile__( \
> > LOCK " decl (%%eax) \n" \
> > - " js "#fail_fn" \n" \
> > + " js 2f \n" \
> > + "1: \n" \
> > + \
> > + LOCK_SECTION_START("") \
> > + "2: call "#fail_fn" \n" \
> > + " jmp 1b \n" \
> > + LOCK_SECTION_END \
> > \
> > :"=a" (dummy) \
> > : "a" (count) \
>
>
> But now it's inefficient again.
>
> Why not this:
>
> LOCK " decl (%%eax) \n" \
> " jns 1f \n" \
> " call "#fail_fn" \n" \
> "1: \n" \
> \
> :"=a" (dummy) \
> : "a" (count) \
>
>
> Will the extra taken forward conditional jump in the fastpath cause much
> of a slowdown?
yeah - the fastpath is much more common than the slowpath.
Ingo
next prev parent reply other threads:[~2006-01-11 10:14 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-11 8:24 Chuck Ebbert
2006-01-11 10:13 ` Ingo Molnar [this message]
-- strict thread matches above, loose matches on Subject: below --
2006-01-12 17:53 Chuck Ebbert
2006-01-10 17:44 i386 FRAME_POINTER needs DEBUG_MUTEXES Hugh Dickins
2006-01-10 21:07 ` [patch] fix i386 mutex fastpath on FRAME_POINTER && !DEBUG_MUTEXES Ingo Molnar
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