Re: [PATCH net] net: stmmac: Fix NAPI poll in TX path when in multi-queue

[David Miller]

From: Jose Abreu <jose.abreu@xxxxxxxxxxxx>
Date: Wed, 13 Feb 2019 18:00:43 +0100

> Commit 8fce33317023 introduced the concept of NAPI per-channel and
> independent cleaning of TX path.
> 
> This is currently breaking performance in some cases. The scenario
> happens when all packets are being received in Queue 0 but the TX is
> performed in Queue != 0.
> 
> I didn't look very deep but it seems that NAPI for Queue 0 will clean
> the RX path but as TX is in different NAPI, this last one is called at a
> slower rate which kills performance in TX. I suspect this is due to TX
> cleaning takes much longer than RX and because NAPI will get canceled
> once we return with 0 budget consumed (e.g. when TX is still not done it
> will return 0 budget).
> 
> Fix this by looking at all TX channels in NAPI poll function.
> 
> Signed-off-by: Jose Abreu <joabreu@xxxxxxxxxxxx>
> Fixes: 8fce33317023 ("net: stmmac: Rework coalesce timer and fix multi-queue races")

No this isn't right.

The TX interrupt events for Queue != 0 should clean up the TX packets
on those queues.

Furthermore you are breaking the locality of the TX processing.

I'm not applying this, sorry.