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Sender: Tejun Heo <htejun@gmail.com>
Date:   Mon, 12 Dec 2022 12:00:19 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     torvalds@linux-foundation.org, mingo@redhat.com,
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Subject: Re: [PATCH 31/31] sched_ext: Add a rust userspace hybrid example
 scheduler
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References: <20221130082313.3241517-1-tj@kernel.org>
 <20221130082313.3241517-32-tj@kernel.org>
 <Y5c0qEuyn8cAvLGQ@hirez.programming.kicks-ass.net>
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Hello,

On Mon, Dec 12, 2022 at 03:03:20PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 29, 2022 at 10:23:13PM -1000, Tejun Heo wrote:
> > From: Dan Schatzberg <dschatzberg@meta.com>
> > 
> > Atropos is a multi-domain BPF / userspace hybrid scheduler where the BPF
> > part does simple round robin in each domain and the userspace part
> > calculates the load factor of each domain and tells the BPF part how to load
> > balance the domains.
> > 
> > This scheduler demonstrates dividing scheduling logic between BPF and
> > userspace and using rust to build the userspace part.
> 
> And here I am, speaking neither Rust nor BPF.

I'm not super fluent in rust but do really enjoy whenever I get to do things
in it. What the language pulls off is actually really neat. It does take
some getting-used-to tho.

> But really, having seen some of this I long for the UMCG patches -- that
> at least was somewhat sane and trivially composes, unlike all this
> madness.

Putting aside lack of familiarity, there are several things which make the
examples including this one not very readable. e.g. how the loops have to be
structured in BPF and the inability to seamlessly access the elements of
certain BPF map types do hamper ergonomics and readability quite a bit. That
said, there are a lot of new developments in BPF which should improve many
of these areas, so hopefully things should keep getting better.

Thanks.

-- 
tejun