From: Chuck Ebbert <cebbert@redhat.com>
To: Nick Piggin <npiggin@suse.de>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andi Kleen <ak@suse.de>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch 1/4] x86: FIFO ticket spinlocks
Date: Thu, 01 Nov 2007 16:01:45 -0400 [thread overview]
Message-ID: <472A30A9.7040203@redhat.com> (raw)
In-Reply-To: <20071101140320.GC26879@wotan.suse.de>
On 11/01/2007 10:03 AM, Nick Piggin wrote:
[edited to show the resulting code]
> + __asm__ __volatile__ (
> + LOCK_PREFIX "xaddw %w0, %1\n"
> + "1:\t"
> + "cmpb %h0, %b0\n\t"
> + "je 2f\n\t"
> + "rep ; nop\n\t"
> + "movb %1, %b0\n\t"
> + /* don't need lfence here, because loads are in-order */
> "jmp 1b\n"
> + "2:"
> + :"+Q" (inc), "+m" (lock->slock)
> + :
> + :"memory", "cc");
> }
If you really thought you might get long queues, you could figure out
how far back you are and use that to determine how long to wait before
testing the lock again. That cmpb could become a subb without adding
overhead to the fast path -- that would give you the queue length (or
its complement anyway.)
next prev parent reply other threads:[~2007-11-01 20:02 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-11-01 14:01 [patch 0/4] ticket spinlocks for x86 Nick Piggin
2007-11-01 14:02 ` [patch 1/4] spinlock: lockbreak cleanup Nick Piggin
2007-11-01 14:06 ` Peter Zijlstra
2007-11-01 14:29 ` Nick Piggin
2007-11-01 15:39 ` Lee Schermerhorn
2007-11-01 15:46 ` Ingo Molnar
2007-11-01 15:53 ` Nick Piggin
2007-11-01 14:03 ` [patch 1/4] x86: FIFO ticket spinlocks Nick Piggin
2007-11-01 14:40 ` Gregory Haskins
2007-11-01 16:38 ` Linus Torvalds
2007-11-02 0:35 ` Rik van Riel
2007-11-02 1:19 ` Linus Torvalds
2007-11-02 2:01 ` Rik van Riel
2007-11-02 6:42 ` Nick Piggin
2007-11-02 14:05 ` Rik van Riel
2007-11-02 22:37 ` Nick Piggin
2007-11-02 15:33 ` Ingo Molnar
2007-11-07 8:46 ` Nick Piggin
2007-11-02 14:24 ` Gregory Haskins
2007-11-01 20:01 ` Chuck Ebbert [this message]
2007-11-02 0:00 ` Nick Piggin
2007-11-02 16:22 ` Chuck Ebbert
2007-11-02 16:51 ` Linus Torvalds
2007-11-02 23:01 ` Nick Piggin
2007-11-03 0:56 ` Chuck Ebbert
2007-11-03 3:41 ` Nick Piggin
2007-11-01 14:04 ` [patch 3/4] x86: spinlock.h merge prep Nick Piggin
2007-11-01 14:05 ` [patch 4/4] x86: spinlock.h merge Nick Piggin
2007-11-03 22:36 ` [patch 0/4] ticket spinlocks for x86 Jeremy Fitzhardinge
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