From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>,
Jes Sorensen <jes@trained-monkey.org>,
Linus Torvalds <torvalds@osdl.org>,
lkml <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@osdl.org>,
Arjan van de Ven <arjanv@infradead.org>,
Zwane Mwaikambo <zwane@arm.linux.org.uk>,
Oleg Nesterov <oleg@tv-sign.ru>,
David Howells <dhowells@redhat.com>,
Alan Cox <alan@lxorguk.ukuu.org.uk>,
Benjamin LaHaise <bcrl@kvack.org>,
Steven Rostedt <rostedt@goodmis.org>,
Christoph Hellwig <hch@infradead.org>, Andi Kleen <ak@suse.de>,
Russell King <rmk+lkml@arm.linux.org.uk>,
Nicolas Pitre <nico@cam.org>
Subject: Re: [patch 0/8] mutex subsystem, ANNOUNCE
Date: Thu, 22 Dec 2005 19:32:57 +1100 [thread overview]
Message-ID: <43AA64B9.8050100@yahoo.com.au> (raw)
In-Reply-To: <1135239672.2940.7.camel@laptopd505.fenrus.org>
Arjan van de Ven wrote:
>>I'd probably just call "bastard": it is probably _unlucky_ when _doesn't_
>>get to retake the lock, judging by the factor-of-4 speedup that Jes
>>demonstrated.
>
>
> I suspect that's more avoiding the double wakeup that semaphores have
> (semaphores aren't quite fair either)
>
It would be great if that were the case.
>
>>Which might be the right thing to do, but having the front waiter go to
>>the back of the queue I think is not.
>
>
> afaik that isn't happening though.
>
AFAIKS it does.
Failed lockers will go through to __mutex_lock_nonatomic, which calls
__mutex_lock_common to queue it on the tail of the FIFO list race-free.
__mutex_lock_nonatomic then sleeps, waiting for the task to become head
of the list and be worken up.
__mutex_lock_nonatomic then removes this task from the FIFO and calls
__mutex_lock_common again.
If I read right, not only is it a fairness problem, but it could also
harm performance because it will cycle through all waiting tasks rather
than just the next one to go.
If I don't read right... can you explain how it works? :P
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
next prev parent reply other threads:[~2005-12-22 8:33 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-21 15:54 [patch 0/8] mutex subsystem, ANNOUNCE Ingo Molnar
2005-12-21 16:04 ` Arjan van de Ven
2005-12-21 18:07 ` Jes Sorensen
2005-12-22 2:36 ` Nick Piggin
2005-12-22 2:57 ` Nick Piggin
2005-12-22 7:19 ` Ingo Molnar
2005-12-22 7:56 ` Nick Piggin
2005-12-22 8:00 ` Arjan van de Ven
2005-12-22 8:10 ` Nick Piggin
2005-12-22 8:21 ` Arjan van de Ven
2005-12-22 8:32 ` Nick Piggin [this message]
2005-12-22 8:24 ` Ingo Molnar
2005-12-22 8:37 ` Nick Piggin
2005-12-21 22:43 ` Nicolas Pitre
2005-12-21 22:43 ` [patch 1/3] mutex subsystem: fix additions to the ARM atomic.h Nicolas Pitre
2005-12-21 22:44 ` [patch 2/3] mutex subsystem: add new atomic primitives Nicolas Pitre
2005-12-21 22:44 ` [patch 3/3] mutex subsystem: move the core to the new atomic helpers Nicolas Pitre
2005-12-21 23:12 ` Ingo Molnar
2005-12-22 1:16 ` Matt Mackall
2005-12-22 6:50 ` Nicolas Pitre
2005-12-22 6:51 ` [patch 2/5] mutex subsystem: add architecture specific mutex primitives Nicolas Pitre
2005-12-22 7:44 ` Nick Piggin
2005-12-22 8:03 ` Nick Piggin
2005-12-22 6:52 ` [patch 1/5] mutex subsystem: fix asm-arm/atomic.h Nicolas Pitre
2005-12-22 6:53 ` [patch 3/5] mutex subsystem: move the core to the new atomic helpers Nicolas Pitre
2005-12-22 6:53 ` [patch 4/5] mutex subsystem: allow architecture defined fast path for mutex_lock_interruptible Nicolas Pitre
2005-12-22 6:53 ` [patch 5/5] mutex subsystem: allow for the fast path to be inlined Nicolas Pitre
2005-12-21 22:36 [patch 0/8] mutex subsystem, ANNOUNCE Ingo Molnar
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