linux-kernel - Re: [PATCH sched_ext/for-6.11 2/2] sched_ext: Implement scx_bpf_consume

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Message-ID: <CAEf4BzY9-CW+SamvwkrHBH1RgB3bxybRmnrK_E0p_Np=V5MsMg@mail.gmail.com>
Date: Fri, 28 Jun 2024 16:56:55 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Tejun Heo <tj@...nel.org>
Cc: Alexei Starovoitov <alexei.starovoitov@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	David Vernet <void@...ifault.com>
Subject: Re: [PATCH sched_ext/for-6.11 2/2] sched_ext: Implement scx_bpf_consume_task()

On Fri, Jun 28, 2024 at 4:13 PM Tejun Heo <tj@...nel.org> wrote:
>
> Hello, again.
>
> On Fri, Jun 28, 2024 at 01:04:04PM -1000, Tejun Heo wrote:
> ...
> > Not a stupid question at all. It's just that all the existing interface is
> > based on IDs. This is partly because there's not much the BPF code can do
> > with the DSQ data structure and partly because DSQs are usually not accessed
> > multiple times in sequence (ie. if the BPF code isn't going to look it up
> > and hold it persistently, it's going to have to look it up each time
> > anyway).
> >
> > The multiple lookups aren't the end of the world. They're all on a resizing
> > hashtable, so lookups should be pretty low cost. It's just a little bit sad
> > to look at.
>
> Just a bit of addition and a question. scx_bpf_consume_task() is maybe named
> too generically and I have a hard time imagining it being useful outside
> iteration loop. So, it does work out kinda neatly if we can tie the whole
> thing (DSQ lookup, barrier seq) to the iterator.
>
> The reason why this becomes nasty is because I can't pass the pointer to the
> iterator to a kfunc, so maybe allowing that can be a solution here too?
>

Sure, if that's the best way to go about this.


> Thanks.
>
> --
> tejun