linux-kernel - Re: [perfmon] Re: [perfmon2] perfmon2 merge news

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Date:	Tue, 13 Nov 2007 13:13:45 -0800
From:	Stephane Eranian <eranian@....hp.com>
To:	William Cohen <wcohen@...hat.com>
Cc:	akpm@...l.org, Robert Richter <robert.richter@....com>,
	gregkh@...e.de, linux-kernel@...r.kernel.org,
	perfmon@...ali.hpl.hp.com, Andi Kleen <andi@...stfloor.org>,
	perfmon2-devel@...ts.sourceforge.net, perfmon@...ali.hpl.hp.com
Subject: Re: [perfmon] Re: [perfmon2] perfmon2 merge news

Will,

On Tue, Nov 13, 2007 at 01:33:55PM -0500, William Cohen wrote:
> 
> The oprofile module can setup a handler for PMU interrupts. This is done in 
> archi/x86/oprofile/nmi_int:nmi_cpu_setup().  Other modules could do the 
> same. However, it bumps what ever was using the nmi/pmu off, then restores 
> nmi/pmu when oprofile is shut down. Maybe the pmu/nmi resource reservation 
> mechanism should be another self-contained patch.
> 

Oprofile does not setup the PMU interrupt. It builds on top of the NMI watchdog
setup. It uses the register_die() mechanism, if I recall. The low level APIC
and gate is setup elsewhere. Perfmon does not use NMI, unless forced to because
of the NMI watchdog. 


> >	- we could not support per-thread mode with the kernel module 
> >	approach due to
> >	  link to the context switch code. I do believe per-thread is a key 
> >	  value-add
> >	  for performance monitoring.
> 
> The per-thread monitoring is useful to a number of people and many people 
> want it. The thought was how to break the large perfmon patch into set of 
> smaller incremental patches. So it isn't whether to have per-thread pmu 
> virtualization, but rather when/how to get it in.

I think we all agree on this.

-- 

-Stephane
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