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

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Message-ID: <085fa11e-ea07-c148-1b32-8a09007ee12b@linux.intel.com>
Date:   Fri, 14 Apr 2023 13:53:24 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Andi Kleen <ak@...ux.intel.com>
Cc:     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 2023-04-14 12:09 p.m., Peter Zijlstra wrote:
> On Fri, Apr 14, 2023 at 11:56:41AM -0400, Liang, Kan wrote:
>>> If it were to only support 4, then
>>> we're in counter scheduling contraint hell again 
>>
>> Unfortunately, yes.
>>
>>> and we need to somehow
>>> group all these things together with the LBR event.
>>
>> Group will bring many limits for the usage. For example, I was told
>> there could be someone wants to use it with multiplexing.
> 
> You can create two groups, each with an LBR event, no?

If we put everything in a group, that will make the enabling much
simpler. I don't think the perf tool needs the order information
anymore. Because the kernel enables the events one by one in a group.
The kernel just need to convert the information from the counter order
to the enabling order and dump to user space.

But if we have two groups with LBR event, the order information is still
required. Why we still want to group things?


Thanks,
Kan