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

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Date:	Wed, 15 Nov 2006 11:40:52 -0500
From:	William Cohen <wcohen@...hat.com>
To:	Andi Kleen <ak@...e.de>
CC:	Eric Dumazet <dada1@...mosbay.com>, Andrew Morton <akpm@...l.org>,
	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>,
	Linus Torvalds <torvalds@...l.org>, discuss@...-64.org,
	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: 2.6.19-rc5: known regressions (v3)

Andi Kleen wrote:
>>On a working kernel on an Opteron, we have normally 4 directories 
>>in /dev/oprofile :
>>
>># ls -ld /dev/oprofile/?
>>drwxr-xr-x 1 root root 0 15. Nov 12:38 /dev/oprofile/0
>>drwxr-xr-x 1 root root 0 15. Nov 12:38 /dev/oprofile/1
>>drwxr-xr-x 1 root root 0 15. Nov 12:38 /dev/oprofile/2
>>drwxr-xr-x 1 root root 0 15. Nov 12:38 /dev/oprofile/3
>>
>>With linux-2.6.19-rc5, the first one (0) is missing and we get 1,2,3
> 
> 
> That's because 0 was never available. It is used by the NMI watchdog.
> The new kernel doesn't give it to oprofile anymore.
> 
> 
>>Maybe the 'bug' is in oprofile tools, that currently expect to find '0'
> 
> 
> Yes, it's likely a user space issue.
> 
> -Andi

OProfile has a simplistic view of the performance monitoring hardware. The 
routines in libop/op_alloc_counter.c determine what set of performance registers 
is available from the processor in use. There is no check to see what registers 
are actually available in the /dev/oprofile directory.

opcontrol executes ophelp to determine which specific counters to count which 
events. The function map_event_to_counter() in libop/op_alloc_counter.c does the 
actual selection. It seems what is needed is for map_event_to_counter() to check 
to see which counters are available and mark the others as unavailable.

-Will
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