linux-kernel - Re: [PATCH v2 06/10] sched/debug: Add support to change sched

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Message-ID: <04215f6c-8f77-40f0-ac61-d004a166553d@nvidia.com>
Date: Thu, 5 Jun 2025 14:45:43 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: Tejun Heo <tj@...nel.org>, Juri Lelli <juri.lelli@...hat.com>
Cc: linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>,
 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>, Andrea Righi <arighi@...dia.com>,
 Changwoo Min <changwoo@...lia.com>
Subject: Re: [PATCH v2 06/10] sched/debug: Add support to change sched_ext
 server params

Hi,

On 6/4/2025 2:40 PM, Tejun Heo wrote:
> On Wed, Jun 04, 2025 at 12:02:11PM +0200, Juri Lelli wrote:
>> Hi Joel,
>>
>> On 02/06/25 14:01, Joel Fernandes wrote:
>>> When a sched_ext server is loaded, tasks in CFS are converted to run in
>>> sched_ext class. Modify the ext server parameters as well along with the
>>> fair ones.
>>>
>>> Re-use the existing interface to modify both ext and fair servers to
>>> keep number of interfaces less (as it is, we have a per-cpu interface).
>>
>> We have a bit of code duplication, don't we

Hmm, I did try to keep the duplication less but I'll give it another try.

>> I wonder if we can do
>> anything early on to prevent mis-alignment between servers in the
>> future.

Sure, let me look into that too.

>>
>> Also, is a single shared interface enough? Is the assumption that either
>> all tasks are FAIR or SCX always guaranteed?
> 
> It's not a guarantee but at least all the current use cases are like that.
> No objection to splitting the interface tho. In fact, for SCX, it may make
> more sense to just make it part of sched_ext_ops, so that each scheduler can
> specify what they want.

I am Ok with having different debugfs entries for different servers, and perhaps
we can reuse the code for both to reduce code duplication. Will work on that next.

thanks,

 - Joel