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

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Date:   Fri, 8 Dec 2017 15:42:10 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiri Olsa <jolsa@...hat.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 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
>
> 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).

>
> 	[jolsa@...va perf]$ grep -r L2_RQSTS.DEMAND_DATA_RD_MISS pmu-events/arch/*
> 	pmu-events/arch/x86/broadwell/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/haswell/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/broadwellde/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/haswellx/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/skylake/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/skylakex/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
> 	pmu-events/arch/x86/broadwellx/cache.json:        "EventName": "L2_RQSTS.DEMAND_DATA_RD_MISS",
>
> thanks,
> jirka

Cheers,
John

>
> .
>