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

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Message-Id: <20061115122118.14fa2177.akpm@osdl.org>
Date:	Wed, 15 Nov 2006 12:21:18 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Andi Kleen <ak@...e.de>
Cc:	Linus Torvalds <torvalds@...l.org>, discuss@...-64.org,
	William Cohen <wcohen@...hat.com>,
	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)

On Wed, 15 Nov 2006 20:23:53 +0100
Andi Kleen <ak@...e.de> wrote:

> 
> > The fact is, it used to work, and the kernel changed interfaces, so now it 
> > doesn't. 
> 
> No, it didn't work. oprofile may have done something, but it 
> just silently killed the NMI watchdog in the process.
> That was never acceptable.

But people could get profiles out.  I know, I've seen them!

> Now we do proper accounting of NMI sources and also proper allocation
> of performance counters.
> 
>  
> > Yes, "oprofile" should be fixed to not depend on that, but the kernel 
> > shouldn't change the interfaces, and we should add back the zero entry.
> 
> That would break the nmi watchdog again.
> 
> Anyways, there is a sysctl to disable the nmi watchdog if someone
> is desperate.
> 
> But I think it is clearly oprofile who did wrong here and needs
> to be fixed.
> 

Is it correct to say that oprofile-on-2.6.18 works, and that
oprofile-on-2.6.19-rc5 does not?

Or is there some sort of workaround for this, or does 2.6.19-rc5 only fail
in some particular scenarios?

If it's really true that oprofile is simply busted then that's a serious
problem and we should find some way of unbusting it.  If that means just
adding a dummy "0" entry which always returns zero or something like that,
then fine.

But we can't just go and bust it.
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