linux-kernel - Re: [RFC PATCH v0.1 0/9] UMCG early preview/RFC patchset

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Date:   Fri, 21 May 2021 09:08:20 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Peter Oskolkov <posk@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-api <linux-api@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Peter Oskolkov <posk@...k.io>,
        Joel Fernandes <joel@...lfernandes.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andrei Vagin <avagin@...gle.com>,
        Jim Newsome <jnewsome@...project.org>
Subject: Re: [RFC PATCH v0.1 0/9] UMCG early preview/RFC patchset

Peter Oskolkov <posk@...gle.com> writes:

> On Thu, May 20, 2021 at 2:17 PM Jonathan Corbet <corbet@....net> wrote:
>>
>> Peter Oskolkov <posk@...gle.com> writes:
>>
>> > As indicated earlier in the FUTEX_SWAP patchset:
>> >
>> > https://lore.kernel.org/lkml/20200722234538.166697-1-posk@posk.io/
>> >
>> > "Google Fibers" is a userspace scheduling framework
>> > used widely and successfully at Google to improve in-process workload
>> > isolation and response latencies. We are working on open-sourcing
>> > this framework, and UMCG (User-Managed Concurrency Groups) kernel
>> > patches are intended as the foundation of this.
>>
>> So I have to ask...is there *any* documentation out there on what this
>> is and how people are supposed to use it?  Shockingly, typing "Google
>> fibers" into Google leads to a less than fully joyful outcome...  This
>> won't be easy for anybody to review if they have to start by
>> reverse-engineering what it's supposed to do.
>
> Hi Jonathan,
>
> There is this Linux Plumbers video: https://www.youtube.com/watch?v=KXuZi9aeGTw
> And the pdf: http://pdxplumbers.osuosl.org/2013/ocw//system/presentations/1653/original/LPC%20-%20User%20Threading.pdf
>
> I did not reference them in the patchset because links to sites other
> than kernel.org are strongly discouraged... I will definitely add a
> documentation patch.

I did look at those - but a presentation from 2013 is going to be of
limited relevance for a 2021 patch set.  In particular, the syscall API
appears to have evolved considerably since then.

> Feel free to reach out to me directly or through this LKML thread if
> you have any questions.
>
> Do you think a documentation patch would be useful at this point, as
> opposed to a free-form email discussion?

Documentation patches can help to guide that discussion; they also need
to be reviewed as well.  So yes, I think they should be present from the
beginning.  But then, that's the position I'm supposed to take :)  This
is a big change to the kernel's system-call API, I don't think that
there can be a proper discussion of that without a description of what
you're trying to do.

Thanks,

jon