linux-kernel - Re: s390 perf events JSONs query

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Date:   Fri, 20 Apr 2018 14:53:27 +0100
From:   John Garry <john.garry@...wei.com>
To:     Thomas-Mich Richter <tmricht@...ux.ibm.com>,
        <brueckner@...ux.vnet.ibm.com>, <tmricht@...ux.vnet.ibm.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        "Namhyung Kim" <namhyung@...nel.org>,
        Linuxarm <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: s390 perf events JSONs query

On 20/04/2018 14:25, Thomas-Mich Richter wrote:
> On 04/20/2018 12:51 PM, John Garry wrote:
>> Hi Hendrik, Thomas,
>>
>> I noticed that in 4.17-rc1 support was included for s390 perf pmu-events. I also notice that the JSONs contain many common (identical actually) events between different chips for this arch.
>>
>> Support was added for factoring out common arch events in https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/tools/perf/pmu-events?h=next-20180420&id=e9d32c1bf0cd7a98358ec4aa1625bf2b3459b9ac
>>
>> ARM64 chips use this feature. I am not familiar with the s390 arch, but do you think you could also use this feature?
>>
>> Thanks,
>> John
>>
>
> I have just played with this feature. I was caught off by this error message:
>
> [root@...lp76 pmu-events]# ./jevents s390 arch /tmp/xxx 100000
> d 0    4096 s390                 arch/s390
> d 1    4096 cf_z14               arch/s390/cf_z14
> f 2    1338 basic.json           arch/s390/cf_z14/basic.json
> ....
> jevents: Ignoring file arch/s390/archevent.json  <---- confusing error message

Let me check if this can be silenced.

>
> jevents: Processing mapfile arch/s390/mapfile.csv
> [root@...lp76 pmu-events]#
>
> I started debugging, until I realized this file is still processed.....
> (Just a side remark).
>
> Anyway the features is nice, but it does not save anything in the resulting
> pmu-events.c file, correct? The events defined in the common archevent.json
> files are just copied into the structures of a specific machine.
>

Yes, the resulting derived pmu-events.c should be the same. In fact, if 
there was naming inconsistencies in JSONs previously, they should now be 
gone.

> The feature saves time and space when you create the machine specific json
> files because it allows you to refer to a common event by name. Cool!
>
> On s390 we do not create the json files manually, but have some scripts to
> create them based on s390 type/model hardware specific input files.

Right, I would say that this is mostly useful when the JSONs are created 
manually, which was the case in the ARM world, but not x86. I didn't 
know about s390.

>
> @Hendirk,
> we could rework our internal tool chain to emit the new "ArchStdEvent"
> keyword for common events, but in the end we do not save anything in the
> resulting pmu-events.c file. And it requires considerable rework to
> support it.
> Given that, I would put it very low priority on your todo list, comments?
>

Cheers,
John