linux-kernel - Re: [discuss] Re: 2.6.19-rc5: known regressions (v3)

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Date:	Thu, 16 Nov 2006 16:47:38 +0100
From:	Andi Kleen <ak@...e.de>
To:	William Cohen <wcohen@...hat.com>
Cc:	Andrew Morton <akpm@...l.org>, Linus Torvalds <torvalds@...l.org>,
	discuss@...-64.org, Eric Dumazet <dada1@...mosbay.com>,
	Komuro <komurojun-mbn@...ty.com>,
	Ernst Herzberg <earny@...4u.de>,
	Andre Noll <maan@...temlinux.org>,
	oprofile-list@...ts.sourceforge.net,
	Jens Axboe <jens.axboe@...cle.com>,
	linux-usb-devel@...ts.sourceforge.net, phil.el@...adoo.fr,
	Adrian Bunk <bunk@...sta.de>, Ingo Molnar <mingo@...hat.com>,
	Alan Stern <stern@...land.harvard.edu>,
	linux-pci@...ey.karlin.mff.cuni.cz,
	Stephen Hemminger <shemminger@...l.org>,
	Prakash Punnoor <prakash@...noor.de>,
	Len Brown <len.brown@...el.com>,
	Alex Romosan <romosan@...orax.lbl.gov>, gregkh@...e.de,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrey Borzenkov <arvidjaar@...l.ru>
Subject: Re: [discuss] Re: 2.6.19-rc5: known regressions (v3)


> What other purposes do you see the performance counters useful for? 

Export one to user space as a cycle counter for benchmarking. RDTSC doesn't 
do this job anymore.

> To collect information on process characteristics so they can be scheduled more efficiently?

That might happen at some point in the future, but i would expect
us to wait for CPUs with more performance counters first.

> Is this going to require sharing the nmi interrupt and knowing which perfcounter 
> register triggered the interrupt to get the correct action?  Currently the 
> oprofile interrupt handler assumes any performance monitoring counter it sees 
> overflowing is something it should count.

Yes. That needs to be fixed.

-Andi

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