Lieber Michal,
Am 13.12.23 um 14:23 schrieb Michal Kubiak:
On Tue, Dec 12, 2023 at 05:50:55PM +0100, Paul Menzel wrote:
On 12/12/23 15:55, Michal Kubiak wrote:
From: Joshua Hay <joshua.a....@intel.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.
Thanks.
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?
[…]
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").
Understood. Maybe you could add a summary of the above to the commit
message or just copy and paste. I guess, it’s better than nothing. And
thank you for upstreaming this.
Kind regards,
Paul
_______________________________________________
Intel-wired-lan mailing list
Intel-wired-lan@osuosl.org
https://lists.osuosl.org/mailman/listinfo/intel-wired-lan
