linux-kernel - Re: [RFC v2] perf: Rewrite core context handling

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Message-ID: <64c55bd4-5792-7222-9724-68ae62d0e98e@amd.com>
Date:   Wed, 24 Aug 2022 13:23:28 +0530
From:   Ravi Bangoria <ravi.bangoria@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     acme@...nel.org, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, namhyung@...nel.org, songliubraving@...com,
        eranian@...gle.com, alexey.budankov@...ux.intel.com,
        ak@...ux.intel.com, mark.rutland@....com, megha.dey@...el.com,
        frederic@...nel.org, maddy@...ux.ibm.com, irogers@...gle.com,
        kim.phillips@....com, linux-kernel@...r.kernel.org,
        santosh.shukla@....com, ravi.bangoria@....com
Subject: Re: [RFC v2] perf: Rewrite core context handling

On 24-Aug-22 12:57 PM, Peter Zijlstra wrote:
> On Wed, Aug 24, 2022 at 10:37:36AM +0530, Ravi Bangoria wrote:
> 
>>> Now, I suppose making that:
>>>
>>>   {-1, NULL, NULL}, {cpu, NULL, NULL}
>>>
>>> could work, but wouldn't iterating the the tree be more expensive than
>>> just finding the sub-trees as we do now?
>>
>> pmu=NULL can be used while scheduling entire context. We can just traverse
>> through all pmu events of both cpu subtrees.
> 
> But imagine the case where we have 50 event for a PMU that can only
> schedule 8. Then we have to iterate 42 events for naught instead of
> directly jumping to the next PMU.

Yes, that needs to be handled. And, IIRC, you proposed maintaining a list
of leftmost event from each pmu subtree.

Thanks,
Ravi