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

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Date:   Mon, 8 Jan 2018 15:08:40 +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 Thu, Jan 04, 2018 at 05:17:56PM +0000, John Garry wrote:

SNIP

> 
> 
> Hi Jirka,
> 
> Sorry for the slow reply.

np, just got back from holidays anyway ;-)

> 
> > > > Won't this all potentially have a big maintainence cost?
> > as Andi said it's mostly just the disk space,
> > which is not big deal
> > 
> > I'm not doing JSON file updates, but I think having
> > simple single dir for platform/cpu could save us some
> > confusion in future
> 
> Understood. But for ARM, which has very standardised architecture events, it
> is good to reduce this event duplication between platforms.
> 
> > 
> > however I won't oppose if you want to add this logic,
> > but please:
> >   - use the list_head ;-)
> 
> Of course
> 
> >   - leave the process_one_file function simple
> >     and separate the level0 processing
> 
> ok, this is how it should look already, albeit a couple of
> process_one_file() modifications. I'll re-check this.
> 
> >   - you are using 'EventCode' as an unique ID to find
> >     the base, but it's not unique for x86, you'll need
> >     to add some other ID scheme that fits to all archs
> 
> Right, so you mentioned earlier using a new keyword token to identify
> whether we use the standard event, so we can go his way - ok?

yes, something like that

> I would also like to mention at this point why I did the event
> pre-processing in jevents, and not a separate script:
> - current build does not transverse the arch tree
> 	- tree transversal for JSON processing is done in jevents
> - a script would mean derived objects, which means:
> 	- makefile changes for derived objects
> 	- jevents would have to deal with derived objects
> - jevents already has support for JSON processing
> 
> The advantage of using a script is that we keep the JSON processing in
> jevents simple.

I don't mind the extra functionality in jevents as long as the current
one keeps on working and the new one works for all archs ;-)

thanks,
jirka