linux-kernel - Re: [Cbe-oss-dev] powerpc/cell/oprofile: fix mutex locking for spu-oprofile

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Date:	Thu, 21 Aug 2008 20:20:10 +1000
From:	Michael Ellerman <michael@...erman.id.au>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	cbe-oss-dev@...abs.org, Robert Richter <robert.richter@....com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev@...abs.org, oprofile-list@...ts.sourceforge.net,
	cel <cel@...ux.vnet.ibm.com>
Subject: Re: [Cbe-oss-dev] powerpc/cell/oprofile: fix mutex locking for
	spu-oprofile

On Thu, 2008-08-21 at 10:14 +0200, Arnd Bergmann wrote:
> On Thursday 21 August 2008, Paul Mackerras wrote:
> > Arnd Bergmann writes:
> > 
> > > Paul, any chance we can still get this into 2.6.27?
> > 
> > Possibly.  We'll need a really good explanation for Linus as to why
> > this is needed (what regression or serious bug this fixes) and why it
> > is late.  Can you send me something explaining that?
> 
> The patch does not fix a regression, the spu-oprofile code basically never
> worked. With the current code in Linux, samples in the profile buffer
> can get corrupted because reader and writer to that buffer use different
> locks for accessing it.

Actually for me it worked[1] a reasonable amount of the time, enough to
be useful. So the spu-oprofile code has always been broken in this way,
but it's not always fatal. So the patch doesn't fix a regression, but it
fixes a serious user-visible bug, which makes it legit rc4 material
IMHO.

[1] that was late last year, so possibly a kernel or two ago.

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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