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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 13 Dec 2022 07:32:33 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
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Subject: Re: [PATCH 14/31] sched_ext: Implement BPF extensible scheduler class
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Hello,

On Tue, Dec 13, 2022 at 11:57:12AM +0100, Peter Zijlstra wrote:
> > Given that UP doesn't need to transfer tasks across, it might be possible to
> > move the whole dispatch operation into ->pick_next_task() but the current
> > state would be different, so it's more complicated and will likely be more
> > brittle.
> 
> That sounds like something is amiss, you fundamentally hold all the
> right locks, there is only one.

Yeah, locking is not the problem on UP. It's more that balance() is before
put_prev_task() and pick_next_task() after, so the %current task state is
different between the two points. I'll see if I can sqaure that from SCX
side. I don't see a reason why it wouldn't be possible but it's likely more
complicated than adding a call in the same spot for UP.

Thanks.

-- 
tejun