Date: Fri, 12 Jun 2009 14:05:07 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Mike Frysinger <vapier@gentoo.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>, Paul Mackerras <paulus@samba.org>,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open
	when supported
Message-ID: <20090612120507.GH16044@elte.hu>
References: <1244806169-12232-1-git-send-email-vapier@gentoo.org>
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* Mike Frysinger <vapier@gentoo.org> wrote:

> If the port does not support HAVE_PERF_COUNTERS, then they can't 
> support the perf_counter_open syscall either.  Rather than forcing 
> everyone to add an ignore (or suffer the warning until they get 
> around to implementing support), only whine about the syscall when 
> applicable.

No, this patch is wrong - it's really easy to add support: just hook 
up the syscall. This should happen for every architecture really, so 
the warning is correct and it should not be patched out.

PMU support is not required to get perfcounters support: if an 
architecture hooks up the syscall it will get generic software 
counters and the tools will work as well.

Profiling falls back to a hrtimer-based sampling method - this is a 
much better fallback than oprofile's fall-back to the timer tick. 
This hrtimer based sampling is dynticks/nohz-correct and can go 
beyond HZ if the architecture supports hrtimers.

Thanks,

	Ingo
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