linux-kernel - Re: Serious problem with ticket spinlocks on ia64

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Message-ID: <20100827134802.GX18967@zorg.emea.sgi.com>
Date:	Fri, 27 Aug 2010 14:48:02 +0100
From:	Hedi Berriche <hedi@....com>
To:	Petr Tesarik <ptesarik@...e.cz>
Cc:	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tony Luck <tony.luck@...el.com>
Subject: Re: Serious problem with ticket spinlocks on ia64

On Fri, Aug 27, 2010 at 14:38 Petr Tesarik wrote:
| Hi everybody,
| 
| SGI has recently experienced failures with the new ticket spinlock
| implementation. Hedi Berriche sent me a simple test case that can
| trigger the failure on the siglock.

One more fact, the problem was introduced by commit

    commit 9d40ee200a527ce08ab8c793ba8ae3e242edbb0e
    Author: Tony Luck <tony.luck@...el.com>
    Date:   Wed Oct 7 10:54:19 2009 -0700

        [IA64] Squeeze ticket locks back into 4 bytes.

Reverting the patch makes the problem go away.

IOW, and as far as testing shows, the first incarnation of the ticket locks
implementation on IA64 (commit 2c8696), the one that used 8 bytes, does not
exhibit this problem.

Cheers,
Hedi.
-- 
Hedi Berriche
Global Product Support
http://www.sgi.com/support
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