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

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Message-Id: <201008280013.19941.ptesarik@suse.cz>
Date:	Sat, 28 Aug 2010 00:13:18 +0200
From:	Petr Tesarik <ptesarik@...e.cz>
To:	"Luck, Tony" <tony.luck@...el.com>
Cc:	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hedi Berriche <hedi@....com>
Subject: Re: Serious problem with ticket spinlocks on ia64

On Friday 27 of August 2010 23:11:55 Luck, Tony wrote:
> > One more idea. The wrap-around case is the only one when the high word is
> > modified. This is in fact the only case when the fetchadd.acq competes
> > with the st2.rel about the actual contents of that location. I don't know
> > if it matters...
>
> I pondered that for a while - but I have difficulty believing that
> fetchadd looks at which bits changed and only writes back the bytes
> that did.

OTOH the counter is only 15-bit, so it also wraps around at 0xfffe7fff, but
I have never seen it fail there. It always fails after the wrap-around from 
0xfffeffff.

Petr Tesarik
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