linux-kernel - Re: [PATCH] Add minimal support for software performance counters for ia64

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Message-Id: <1250698351.8282.106.camel@twins>
Date:	Wed, 19 Aug 2009 18:12:31 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	William Cohen <wcohen@...hat.com>
Cc:	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add minimal support for software performance counters
 for ia64

On Wed, 2009-08-19 at 12:04 -0400, William Cohen wrote:
> +#ifdef __ia64__
> +#include "../../arch/ia64/include/asm/unistd.h"
> +#define rmb()          asm volatile("" ::: "memory")
> +#define cpu_relax()    asm volatile("" ::: "memory");
> +#endif

Surely the itanic has a real memory barrier? The kernel seems to use
something along the lines of mf.

Also, cpu_relax() seems to end up being asm volatile("hint @pause" :::
"memory"), although we don't seem to have an actual user of cpu_relax()
in perf atm.



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