Re: [PATCH] arm: perf: Add event descriptions

[Christopher Covington]

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

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