netdev - Re: [Bloat] Trying to *really* understand Linux pacing

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Message-ID: <CAA93jw6di-ypNHH0kz70mhYitT_wsbpZR4gMbSx7FEpSvHx3qg@mail.gmail.com>
Date: Wed, 7 Feb 2024 07:05:27 -0500
From: Dave Taht <dave.taht@...il.com>
To: Michael Welzl <michawe@....uio.no>, 
	Linux Kernel Network Developers <netdev@...r.kernel.org>
Cc: bloat@...ts.bufferbloat.net
Subject: Re: [Bloat] Trying to *really* understand Linux pacing

Dear Michael:

Thank you for digging deeply into packet pacing, TSQ, etc. I think
there are some interesting new possibilities in probing (especially
during slow start) that could make the core idea even more effective
than it is. I also tend to think that attempting it in various cloudy
environments and virtualization schemes, and with certain drivers, the
side effects are not as well understood as I would like. For example,
AWS's nitro lacks BQL as does virtio-net.

I think the netdev community, now cc'd, would be interested in your
document and explorations so far, below. I hope for more
enlightenment.

On Wed, Feb 7, 2024 at 6:57 AM Michael Welzl via Bloat
<bloat@...ts.bufferbloat.net> wrote:
>
> Dear de-bloaters of buffers,
> Esteemed experts of low delay and pacing!
>
> I have no longer been satisfied with high-level descriptions of how pacing works in Linux, and how it interacts with TSQ (I’ve seen some, in various papers, over the years) - but I wanted to REALLY understand it. So, I have dug through the code.
>
> I documented this experience here:
> https://docs.google.com/document/d/1-uXnPDcVBKmg5krkG5wYBgaA2yLSFK_kZa7xGDWc7XU/edit?usp=sharing
> but it has some holes and may have mistakes.
>
> Actually, my main problem is that I don’t really know what goes on when I configure a larger IW… things seem to get quite “off” there. Why? Anyone up for solving that riddle?  ;-)
> (see the tests I documented towards the end of the document)
>
> Generally, if someone who has their hands on files such as tcp_output.c all the time could take a look, and perhaps “fill” my holes, or improve anything that might be wrong, that would be fantastic!   I think that anyone should be allowed to comment and make suggestions in this doc.
>
> MANY thanks to whoever finds the time to take a look !
>
> Cheers,
> Michael
>
> _______________________________________________
> Bloat mailing list
> Bloat@...ts.bufferbloat.net
> https://lists.bufferbloat.net/listinfo/bloat



-- 
40 years of net history, a couple songs:
https://www.youtube.com/watch?v=D9RGX6QFm5E
Dave Täht CSO, LibreQos