linux-kernel - Re: [PATCH 1/2] perf tools: allow building for ARM

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Message-ID: <20091211104126.GA22079@elte.hu>
Date:	Fri, 11 Dec 2009 11:41:26 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	David Miller <davem@...emloft.net>
Cc:	jamie.iles@...ochip.com, linux-kernel@...r.kernel.org,
	linux@....linux.org.uk, peterz@...radead.org
Subject: Re: [PATCH 1/2] perf tools: allow building for ARM


* David Miller <davem@...emloft.net> wrote:

> From: Ingo Molnar <mingo@...e.hu>
> Date: Fri, 11 Dec 2009 11:23:16 +0100
> 
> > 
> > * Jamie Iles <jamie.iles@...ochip.com> wrote:
> > 
> >> +#ifdef __arm__
> >> +#include "../../arch/arm/include/asm/unistd.h"
> >> +#define rmb()		asm volatile("":::"memory")
> >> +#define cpu_relax()	asm volatile("":::"memory")
> >> +#endif
> > 
> > cpu_relax() looks fine, but rmb() seems not to match the one that can be 
> > found in arch/arm/:
> 
> I think he did it this way so it can compile in the meantime, and that 
> doing it right requires runtime cpu detection to select which barrier 
> instruction is even available on the current ARM cpu.

Yeah. We can merge a quick patch for it if runtime detection is 
difficult - but if then such a patch should err on the side of using the 
barrier instruction unconditionally - even if this causes perf to 
segfault on certain (older? UP configured?) ARM cores.

	Ingo
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