[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZXmwR4s25afUbwz3@localhost.localdomain>
Date: Wed, 13 Dec 2023 14:23:19 +0100
From: Michal Kubiak <michal.kubiak@...el.com>
To: Paul Menzel <pmenzel@...gen.mpg.de>
CC: Joshua Hay <joshua.a.hay@...el.com>, <intel-wired-lan@...ts.osuosl.org>,
<maciej.fijalkowski@...el.com>, <emil.s.tantilov@...el.com>,
<larysa.zaremba@...el.com>, <netdev@...r.kernel.org>,
<aleksander.lobakin@...el.com>, <alan.brady@...el.com>, Przemek Kitszel
<przemyslaw.kitszel@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-net] idpf: enable WB_ON_ITR
On Tue, Dec 12, 2023 at 05:50:55PM +0100, Paul Menzel wrote:
> Dear Michal, dear Joshua,
>
>
> Thank you for your patch.
>
> On 12/12/23 15:55, Michal Kubiak wrote:
> > From: Joshua Hay <joshua.a.hay@...el.com>
> >
> > Tell hardware to writeback completed descriptors even when interrupts
>
> Should you resend, the verb is spelled with a space: write back.
Sure, I will fix it.
>
> > are disabled. Otherwise, descriptors might not be written back until
> > the hardware can flush a full cacheline of descriptors. This can cause
> > unnecessary delays when traffic is light (or even trigger Tx queue
> > timeout).
>
> How can the problem be reproduced and the patch be verified?
>
>
> Kind regards,
>
> Paul
>
>
Hi Paul,
To be honest, I have noticed the problem during the implementation of
AF_XDP feature for IDPF driver. In my scenario, I had 2 Tx queues:
- regular LAN Tx queue
- and XDP Tx queue
added to the same q_vector attached to the same NAPI, so those 2 Tx
queues were handled in the same NAPI poll loop.
Then, when I started a huge Tx zero-copy trafic using AF_XDP (on the XDP
queue), and, at the same time, tried to xmit a few packets using the second
(non-XDP) queue (e.g. with scapy), I was getting the Tx timeout on that regular
LAN Tx queue.
That is why I decided to upstream this fix. With disabled writebacks,
there is no chance to get the completion descriptor for the queue where
the traffic is much lighter.
I have never tried to reproduce the scenario described by Joshua
in his original patch ("unnecessary delays when traffic is light").
Thanks,
Michal
Powered by blists - more mailing lists