linux-kernel - Re: [PATCH 0/2] sched_ext: Add a core event and update scx schedulers

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Message-ID: <Z6Wt0kV6IPBbIGk8@gpd3>
Date: Fri, 7 Feb 2025 07:53:06 +0100
From: Andrea Righi <arighi@...dia.com>
To: Changwoo Min <changwoo@...lia.com>
Cc: tj@...nel.org, void@...ifault.com, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] sched_ext: Add a core event and update scx schedulers

On Fri, Feb 07, 2025 at 03:49:24PM +0900, Changwoo Min wrote:
> Hello,
> 
> On 25. 2. 7. 15:24, Andrea Righi wrote:
> > Hi,
> > 
> > On Fri, Feb 07, 2025 at 12:13:36PM +0900, Changwoo Min wrote:
> > > This patchset introduces a new event, SCX_EV_ENQ_SLICE_DFL, and updates
> > > two scx schedulers -- scx_qmap and scx_central -- to print out the new
> > > event.
> > > 
> > > SCX_EV_ENQ_SLICE_DFL counts how many times the tasks' time slice is set
> > > to the default value (SCX_SLICE_DFL) by the sched_ext core in the enqueue
> > > and pick_next paths.
> > > 
> > > Scheduling a task with SCX_SLICE_DFL unintentionally would be a source
> > > of latency spikes because SCX_SLICE_DFL is relatively long (20 msec).
> > > Thus, soaring the SCX_EV_ENQ_SLICE_DFL value would be a sign of BPF
> > > scheduler bugs, causing latency spikes.
> > 
> > Not directly related to this patch set, but as a general thought: would it
> > be useful to introduce ops->slice_ms (in sched_ext_ops) to override
> > SCX_SLICE_DFL?
> > 
> > With that, schedulers that care about latency could set a smaller default
> > time slice to prevent potential spikes caused by the implicit use of
> > SCX_SLICE_DFL.
> > 
> > Opinions?
> 
> That sounds like a good idea!

Alright, I'll send a patch after this one is applied.

Thanks,
-Andrea

> 
> Regards,
> Changwoo Min