linux-kernel - Re: [PATCH v3 2/5] sched_ext: Manage the validity of scx_rq

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Message-ID: <ea78741a-09d6-42b6-b106-9fa5a54ed0fa@igalia.com>
Date: Wed, 4 Dec 2024 10:42:13 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Tejun Heo <tj@...nel.org>, Changwoo Min <multics69@...il.com>
Cc: void@...ifault.com, mingo@...hat.com, peterz@...radead.org,
 kernel-dev@...lia.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/5] sched_ext: Manage the validity of scx_rq_clock

Hello,

On 24. 12. 4. 08:26, Tejun Heo wrote:
> Hello,
> 
> On Tue, Dec 03, 2024 at 11:27:59PM +0900, Changwoo Min wrote:
>> An rq clock becomes valid when it is updated using update_rq_clock()
>> and invalidated when the rq is unlocked using rq_unpin_lock(). Also,
>> after long-running operations -- ops.running() and ops.update_idle() --
>> in a BPF scheduler, the sched_ext core invalidates the rq clock.
> 
> Hmm... why are ops.running() or ops.update_idle() special? ie. How does
> sched_ext core determine what are long-running and what are not.

I investigated all sched_ext_ops. Besides these two ops, all the
rest are control operations, of which BPF operation should be
relatively simple. On the other hand, ops.running() and
ops.update_idle() are different from the others since a CPU
executes a task or becomes idle, which could be arbitrarily long.
So I think refreshing the clock in those cases would be nice.
Does it make sense to you?

Regards,
Changwoo Min