Re: [PATCH] arm: perf: Add event descriptions
From: Drew Richardson
Date: Thu Sep 24 2015 - 13:30:59 EST
On Mon, Aug 17, 2015 at 10:40:35PM +0100, Drew Richardson wrote:
> On Wed, Aug 26, 2015 at 05:51:49PM +0100, Will Deacon wrote:
> > On Mon, Aug 17, 2015 at 09:58:09PM +0100, Drew Richardson wrote:
> > > On Tue, Aug 04, 2015 at 01:15:23AM +0100, Drew Richardson wrote:
> > > > Add additional information about hardware events to make counters self
> > > > describing. This makes the hardware PMUs easier to use as perf list
> > > > contains the possible events instead of users having to refer to
> > > > documentation like the ARM TRMs. This could also allow tools like
> > > > oprofile to support PMUs without requiring an update.
> > > >
> > > > Signed-off-by: Drew Richardson <drew.richardson@xxxxxxx>
> > > > ---
> > > > arch/arm/kernel/perf_event.c | 1 +
> > > > arch/arm/kernel/perf_event_v7.c | 617 ++++++++++++++++++++++++++++++++++++++++
> > > > 2 files changed, 618 insertions(+)
> > >
> > > Any concerns with merging this?
> > We should revisit this after the merge window (since the ARM perf code is
> > moving out to drivers/)
> Not a problem
> > but I do have reservations about putting all these
> > strings into the kernel. Why can't we put this into something like libpfm
> > instead?
> > Will
> My intent is to make it easier for people to use hardware counters on
> ARM, particularly with new CPUs. Currently, the developer of the tool
> needs to extract the event information from the ARM TRMs, add it to
> their tool and make a new release. This work is done by multiple
> tools, for example for the Cortex-A15:
> There are likely more tools, these are the ones I could easily
> find. Note that the new ARM Cortex-A72 isn't supported by most of
> them. And the perf command line tool doesn't have any of this.
> Once the tool supports the new CPUs events the user needs to make sure
> they're running a recent version of the tool that contains these
> events for their new ARM CPU. Technically the user could add the event
> information themselves and upstream the change, but not all users will
> do this.
> So my suggestion to solve the problem is that the kernel can have the
> list of events as proposed in the patch. This is already done for some
> PMUs like arm-ccn and arm-cci. If the tool doesn't support the
> particular CPU, they can fall back to the event list provided by the
> kernel. There will be some information missing like user-friendly
> descriptions of the events, but it's hopefully enough that users can
> do what they need to do and update their tool at a later time.
> I'd be glad to wrap this all in a config option so users can disable
> it to reduce bloat. Perhaps there is some other central location
> outside the kernel that could store this information?
Have you had a chance to review this again? I also noticed that my x86
machines have something similar, although not as few events as I'm
proposing to add.
$ ls /sys/bus/event_source/devices/cpu/events/
cycles-ct el-capacity el-start tx-abort tx-conflict
cycles-t el-commit mem-loads tx-capacity tx-start
el-abort el-conflict mem-stores tx-commit
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