netdev - Re: [RFC PATCH net-next 0/7] NIC driver Rx ring ECN

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Message-ID: <2ff79a56-bf32-731b-a6ab-94654b8a3b31@redhat.com>
Date:   Thu, 12 Jan 2023 14:06:50 +0000
From:   Jeremy Harris <jeharris@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org
Subject: Re: [RFC PATCH net-next 0/7] NIC driver Rx ring ECN

On 11/01/2023 18:46, Jakub Kicinski wrote:
> Do you have any reason to believe that it actually helps anything?

I've not measured actual drop-rates, no.

> NAPI with typical budget of 64 is easily exhausted (you just need
> two TSO frames arriving at once with 1500 MTU).

I see typical systems with 300, not 64 - but it's a valid point.
It's not the right measurement to try to control.
Perhaps I should work harder to locate the ring size within
the bnx2 and bnx2x drivers.

If I managed that (it being already the case for the xgene example)
would your opinions change?

> Host level congestion is better detected using time / latency signals.
> Timestamp the packet at the NIC and compare the Rx time to current time
> when processing by the driver.
> 
> Google search "Google Swift congestion control".

Nice, but
- requires we wait for timestamping-NICs
- does not address Rx drops due to Rx ring-buffer overflow

-- 
Cheers,
   Jeremy