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

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Message-ID: <4A8C4CAA.5070101@redhat.com>
Date:	Wed, 19 Aug 2009 15:04:10 -0400
From:	William Cohen <wcohen@...hat.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
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

Peter Zijlstra wrote:
> 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.
> 
> 
> 

Peter, thanks for the comment. I took a look at the rmb() and cpu_relax() code
in the kernel and revised the patch with the appropriate defines

-Will

View attachment "perf_ia64b.patch" of type "text/plain" (4011 bytes)