netdev - Re: [RFC PATCH net-next 0/1] ibmveth: Implement BQL

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Message-ID: <CAA93jw5reJmaOvt9vw15C1fo1AN7q5jVKzUocbAoNDC-cpi=KQ@mail.gmail.com>
Date:   Tue, 25 Oct 2022 17:08:26 -0700
From:   Dave Taht <dave.taht@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Nick Child <nnac123@...ux.ibm.com>, netdev@...r.kernel.org,
        nick.child@....com
Subject: Re: [RFC PATCH net-next 0/1] ibmveth: Implement BQL

On Tue, Oct 25, 2022 at 3:10 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Tue, 25 Oct 2022 15:03:03 -0500 Nick Child wrote:
> > Th qdisc is default pfifo_fast.
>
> You need a more advanced qdisc to seen an effect. Try fq.
> BQL tries to keep the NIC queue (fifo) as short as possible
> to hold packets in the qdisc. But if the qdisc is also just
> a fifo there's no practical difference.
>
> I have no practical experience with BQL on virtualized NICs
> tho, so unsure what gains you should expect to see..

fq_codel would be a better choice of underlying qdisc for a test, and
in this environment you'd need to pound the interface flat with hundreds
of flows, preferably in both directions.

My questions are:

If the ring buffers never fill, why do you need to allocate so many
buffers in the first place?
If bql never engages, what's the bottleneck elsewhere? XMIT_MORE?

Now the only tool for monitoring bql I know of is bqlmon.

-- 
This song goes out to all the folk that thought Stadia would work:
https://www.linkedin.com/posts/dtaht_the-mushroom-song-activity-6981366665607352320-FXtz
Dave Täht CEO, TekLibre, LLC