linux-kernel - Re: [RFC PATCH 2/5] perf jevents: add support for arch recommended events

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Date:   Sat, 9 Dec 2017 08:31:04 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        ak@...ux.intel.com, wcohen@...hat.com, will.deacon@....com,
        ganapatrao.kulkarni@...ium.com, catalin.marinas@....com,
        mark.rutland@....com, xuwei5@...ilicon.com, linuxarm@...wei.com,
        zhangshaokun@...ilicon.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 2/5] perf jevents: add support for arch recommended
 events

On Fri, Dec 08, 2017 at 03:42:10PM +0000, John Garry wrote:
> On 08/12/2017 12:29, Jiri Olsa wrote:
> > On Wed, Dec 06, 2017 at 03:20:14PM +0000, John Garry wrote:
> > > On 06/12/2017 13:36, Jiri Olsa wrote:
> > > > On Wed, Dec 06, 2017 at 12:13:16AM +0800, John Garry wrote:
> > > > > For some architectures (like arm64), there are architecture-
> > > > > defined recommended events. Vendors may not be obliged to
> > > > > follow the recommendation and may implement their own pmu
> > > > > event for a specific event code.
> > > > > 
> > > > > This patch adds support for parsing events from arch-defined
> > > > > recommended JSONs, and then fixing up vendor events when
> > > > > they have implemented these events as recommended.
> > > > 
> > > > in the previous patch you added the vendor support, so
> > > > you have arch|vendor|platform key for the event list
> > > > and perf have the most current/local event list
> > > > 
> > > > why would you need to fix it? if there's new event list,
> > > > the table gets updated, perf is rebuilt.. I'm clearly
> > > > missing something ;-)
> > > 
> > > The 2 patches are quite separate. In the first patch, I just added support
> > > for the vendor subdirectory.
> > > 
> > > So this patch is not related to rebuilding when adding a new event list or
> > > dependency checking.
> > > 
> > > Here we are trying to allow the vendor to just specify that an event is
> > > supported as standard in their platform, without duplicating all the
> > > standard event fields in their JSON. When processing the vendor JSONs, the
> > > jevents tool can figure which events are standard and create the proper
> > > event entries in the pmu events table, referencing the architecture JSON.
> > 
> 
> Hi jirka,
> 
> > I think we should keep this simple and mangle this with some pointer logic

sry for confusion, of course it should have been '.. and NOT mangle..' ;-)

> > 
> > now you have arch/vendor/platform directory structure..
> 
> I'm glad that there seems to be no objection to this, as I feel that this
> was a problem.
> 
> why don't
> > you add events for every such directory? I understand there will
> > be duplications, but we already have them for other archs and it's
> > not big deal:
> 
> The amount of duplication was the concern. As mentioned earlier, it would be
> anticipated that every vendor would implement these events as recommended,
> so a copy for every platform from every vendor. We're looking for a way to
> avoid this.
> 
> Actually having a scalable JSON standard format for pmu events, which allows
> us to define common events per architecture / vendor and reference them per
> platform JSON could be useful.
> 
> Here we're dealing with trade-off between duplication (simplicity) vs
> complexity (or over-engineering).

understood, but as I said we already are ok with duplicates,
if it's reasonable size as is for x86 now..  how much amount
are we talking about for arm?

jirka