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

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Message-ID: <20090821142514.GE11098@elte.hu>
Date:	Fri, 21 Aug 2009 16:25:14 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	William Cohen <wcohen@...hat.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add minimal support for software performance counters
	for ia64


* William Cohen <wcohen@...hat.com> wrote:

> Peter Zijlstra wrote:
> > On Wed, 2009-08-19 at 15:04 -0400, William Cohen wrote:
> >> 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
> > 
> > Looks good now, thanks!
> > 
> 
> When looking through the patch today I realized the new 
> perf_counter.h was placed in include/asm-ia64. It should be placed 
> in arch/ia64/include/asm/perf_counter.h.

mind sending out a v2 patch with all review feedback folded in, for 
IA64 maintainers to ack if they like it?

Thanks,

	Ingo
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