linux-kernel - Re: [PATCH 1/1] ARM: oprofile: add A5/A7/A15 entries in op_perf

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Message-ID: <20121120170817.GG27765@mudshark.cambridge.arm.com>
Date:	Tue, 20 Nov 2012 17:08:17 +0000
From:	Will Deacon <will.deacon@....com>
To:	Robert Richter <rric@...nel.org>
Cc:	Maynard Johnson <maynardj@...ibm.com>,
	"jgq516@...il.com" <jgq516@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"oprofile-list@...ts.sf.net" <oprofile-list@...ts.sf.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/1] ARM: oprofile: add A5/A7/A15 entries in op_perf_name

On Tue, Nov 20, 2012 at 05:06:01PM +0000, Robert Richter wrote:
> On 20.11.12 16:55:17, Will Deacon wrote:
> > On Tue, Nov 20, 2012 at 04:31:58PM +0000, Robert Richter wrote:
> > > I am thinking of the following:
> > > 
> > >  # cat /root/cpu_type
> > >  arm/armv7-ca5
> > >  # cat /dev/oprofile/cpu_type
> > >  unknown
> > >  # mount --bind /root/cpu_type /dev/oprofile/cpu_type
> > >  # cat /dev/oprofile/cpu_type
> > >  arm/armv7-ca5
> > > 
> > > From here legacy oprofile tools work as expected using oprofilefs. (I
> > > think. Did not test it.) We need to change the kernel for this a bit
> > > to return 'unknown'. The mount could be done by the oprofile tools
> > > using existing cpu detection code. This is only one way to setup
> > > cpu_type from userland, there could be other ways too.
> > 
> > Ok, this is functionally equivalent to the patch that was submitted at the
> > start of this thread: it solves the problem of mapping a single ARM core to
> > a oprofile's CPU ID string. Technically, I don't mind doing that in the
> > kernel (at least, it means you don't need to do your trick above)
> 
> The advantage of a solution where userland updates cpu_type is that we
> never need to update the kernel anymore. This means, cpu detection can
> be part of the tools.

True, but the kernel-side perf code still needs updating to support the new
CPU so I don't think you win much.

Will
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