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

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Message-Id: <201008271837.10014.ptesarik@suse.cz>
Date:	Fri, 27 Aug 2010 18:37:08 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	Hedi Berriche <hedi@....com>
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 Friday 27 of August 2010 16:52:31 Hedi Berriche wrote:
> On Fri, Aug 27, 2010 at 15:40 Petr Tesarik wrote:
> | On Friday 27 of August 2010 16:31:35 Hedi Berriche wrote:
> | > That said, I'm letting my already over 36 hours run carry on chewing
> | > CPU time, and see if it will eventually trip the same problem seen with
> | > 4-byte ticket locks.
> |
> | Hm, this doesn't sound like a viable approach. Since the siglock gets
> | initialized to 0 when a new process is started, it may never actually
> | wrap around.
> |
> | I would rather attach a SystemTap probe somewhere during process fork and
> | add a bias to the siglock. That should work fine. Let me knock up the
> | SystemTap script...
>
> That would be nice. Ta!

Here it is. I don't have a system with the old 64-bit ticket spinlocks at 
hand, so this is completely untested, but it should work fine.

Adjust if needed.

Petr

View attachment "biaslock.stp" of type "text/x-csrc" (456 bytes)