linux-kernel - Re: [PATCH RFC 3/8] sched/ext: Add a DL server for sched

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Message-ID: <3b244939-6d55-4d86-8b77-a9a7629f8239@nvidia.com>
Date: Sat, 15 Mar 2025 19:15:27 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, Andrea Righi <arighi@...dia.com>,
 Tejun Heo <tj@...nel.org>, Ingo Molnar <mingo@...hat.com>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 David Vernet <void@...ifault.com>, Changwoo Min <changwoo@...lia.com>,
 Luigi De Matteis <ldematteis123@...il.com>, paulmck@...nel.org,
 boqun.feng@...il.com
Subject: Re: [PATCH RFC 3/8] sched/ext: Add a DL server for sched_ext tasks



On 3/15/2025 3:22 AM, Peter Zijlstra wrote:
> On Fri, Mar 14, 2025 at 10:21:50PM -0400, Joel Fernandes wrote:
>> sched_ext currently suffers starvation due to RT. The same workload when
>> converted to EXT can get zero runtime if RT is 100% running, causing EXT
>> processes to stall. Fix it by adding a DL server for EXT.
> 
> This needs a lot more words on why you need a second server. Because I
> don't think you do.

Sure, I will add more words to the change log to explain rationale. When you say
"I don't think you do", do you mean that both FAIR and EXT could be served by
the same server? If so, that will not handle the case where the system has both
FAIR and EXT tasks in the mix (EXT has a partial mode where certain tasks can be
made EXT with certain others left as FAIR) and FAIR runs 100% and starves EXT.
We still need bandwidth allocated to EXT in such a situation. So we do need an
EXT server. Or did you mean something else?

thanks,

 - Joel