linux-kernel - Re: [PATCH] arm: perf: Add event descriptions

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Date:	Tue, 27 Oct 2015 11:46:12 -0400
From:	Christopher Covington <cov@...eaurora.org>
To:	Will Deacon <will.deacon@....com>,
	Drew Richardson <Drew.Richardson@....com>
CC:	Russell King <linux@....linux.org.uk>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Wade Cherry <Wade.Cherry@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm: perf: Add event descriptions

On 10/07/2015 07:20 AM, Will Deacon wrote:
> Hi again, Drew,
> 
> On Thu, Sep 24, 2015 at 06:52:57PM +0100, Will Deacon wrote:
>> On Mon, Aug 17, 2015 at 10:40:36PM +0100, Drew Richardson wrote:
>>> So my suggestion to solve the problem is that the kernel can have the
>>> list of events as proposed in the patch.
>>
>> Sorry, but I just don't buy this argument. Your problem is that the user
>> needs to be running an up-to-date perf tool, but with your proposed
>> solution, you're asking them to update the *kernel* instead, which is
>> (unfortunately) one of the hardest pieces of software to upgrade on a
>> typical ARM platform.
> 
> I've spent some time thinking about this and, actually, it makes sense
> to do this for the architected events. These event numbers are guaranteed
> to be portable between CPUs, so if we expose those through sysfs then
> we don't have this dependency on updating the kernel for newer cores
> (well, once the initial period without your patch has expired). It's the
> noon-portable, micro-architectural events that I object to.
> 
> So how about you roll a new version of this patch just exposing the
> architected events and making use of the macros in perf_event.h to make
> it a bit tidier (PMU_EVENT_ATTR, PMU_EVENT_ATTR_STRING etc)?
> 
> Be aware that there's a fair amount of arm64 perf patches queue for 4.4,
> since we're moving over to the code in drivers/perf/. Hopefully these
> will appear on the arm64 for-next/core branch shortly.

Have you considered using OF/ACPI to describe this aspect of the hardware?

Thanks,
Christopher Covington

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
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