linux-kernel - Re: [PATCH] seqlock: serialize against writers

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Message-ID: <20080829162216.GW26610@one.firstfloor.org>
Date:	Fri, 29 Aug 2008 18:22:16 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Gregory Haskins <gregory.haskins@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Gregory Haskins <ghaskins@...ell.com>, mingo@...e.hu,
	rostedt@...dmis.org, tglx@...utronix.de,
	linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [PATCH] seqlock: serialize against writers

> Im running it on a x86_64 box as we speak.  How can I tell if there is a
> certain mode that is permitting this?

If the boot up says you're running with PMtimer then it uses the fallback
(usually happens on pre Fam10h AMD boxes). A typical Intel box
would use the faster ring 3 only TSC path and then explode with your
change I bet. 

Or step with gdb through gettimeofday() and see if it does a syscall.

-Andi
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