linux-kernel - Re: [PATCH 2/6] perf: Support branch events logging

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Message-ID: <b008c6c8-5c6a-7a65-d123-058d7e8456b0@linux.intel.com>
Date:   Mon, 17 Apr 2023 06:37:20 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Liang, Kan" <kan.liang@...ux.intel.com>, mingo@...hat.com,
        acme@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
        adrian.hunter@...el.com, eranian@...gle.com
Subject: Re: [PATCH 2/6] perf: Support branch events logging


On 4/17/2023 4:46 AM, Peter Zijlstra wrote:
> On Fri, Apr 14, 2023 at 03:47:29PM -0700, Andi Kleen wrote:
>>> Yeah, don't do this. There is no guarantee what so ever you'll get any
>>> of those events in the 0-3 range.
>>
>> The kernel can simply force to 0-3 if LBR is enabled and the feature too.
>> It's in Kan's patch
>>
>> and it isn't particularly complicated.
> And what, totally leave 4-7 unused even if those counters were not
> related to LBR at all? That seems exceedingly daft.


Only for the events which enabled LBR and also only if the branch events 
feature is enabled

-j event -e '{event1:b,event2:b,event3:b,event4:b,event5,event6}'

event5 and 6 can go > 3

Given there is currently no syntax to control branch events inside a 
group other than fully enabling/disabling LBR.

Kan, I guess that could be added to the user tools.

-Andi