linux-kernel - Re: [PATCH 04/29] x86/perfcounters: rework pmc_amd_save_disable_all() and pmc_amd_restore

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Message-ID: <18936.18732.35199.647196@cargo.ozlabs.ibm.com>
Date:	Wed, 29 Apr 2009 22:33:48 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Robert Richter <robert.richter@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/29] x86/perfcounters: rework
	pmc_amd_save_disable_all() and pmc_amd_restore_all()

Ingo Molnar wrote:

> Could we remove the disable-all facility altogether and make the 
> core code NMI-safe? The current approach wont scale on CPUs that 
> dont have global-disable features.
> 
> disable-all was arguably a hack i introduced and which spread too 
> far. Can you see a conceptual need for it?

If you're talking about hw_perf_save_disable / hw_perf_restore, please
don't get rid of those.  I use them to batch up counter enable/disable
operations so I only have to compute the PMU config once for each
batch rather than every time an individual counter is enabled or
disabled.

Paul.
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