linux-kernel - Re: [PATCHSET v4] sched: Implement BPF extensible scheduler class

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Message-ID: <ZLrQdTvzbmi5XFeq@slm.duckdns.org>
Date:   Fri, 21 Jul 2023 08:37:41 -1000
From:   Tejun Heo <tj@...nel.org>
To:     torvalds@...ux-foundation.org, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...nel.org,
        joshdon@...gle.com, brho@...gle.com, pjt@...gle.com,
        derkling@...gle.com, haoluo@...gle.com, dvernet@...a.com,
        dschatzberg@...a.com, dskarlat@...cmu.edu, riel@...riel.com
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        kernel-team@...a.com
Subject: Re: [PATCHSET v4] sched: Implement BPF extensible scheduler class

Hello,

It's been more than half a year since the initial posting of the patchset
and we are now at the fourth iteration. There have been some reviews around
specifics (should be all addressed now except for the ones Andrea raised on
this iteration) but none at high level. There also were some in-person and
off-list discussions. Some, I believe, are addressed by the cover letter but
it'd be nonetheless useful to delve into them on-list.

On our side, we've been diligently experimenting. A lot of our earlier
experiments were focused on improving work conservation which led to the CFS
shared runqueue patchset that David Vernet is currently working on. The
workqueue experiments which led to PeterZ's SIS_NODE patch was also informed
by the same work conservation experiments. We also played with soft affinity
which is inspired by Julia's nest scheduler. Another thing we recently
learned was that at least for our web workload, L1/2 locality doesn't matter
much. This is an area of on-going experiments.

We are comfortable with the current API. Everything we tried fit pretty
well. It will continue to evolve but sched_ext now seems mature enough for
initial inclusion. I suppose lack of response doesn't indicate tacit
agreement from everyone, so what are you guys all thinking?

Thanks.

--
tejun