netdev - Re: [PATCH net-next v3 0/4] Add support to do threaded napi busy poll

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Message-ID: <Z6TAt7HIA4Sj5uep@LQ3V64L9R2>
Date: Thu, 6 Feb 2025 06:01:27 -0800
From: Joe Damato <jdamato@...tly.com>
To: Samiullah Khawaja <skhawaja@...gle.com>
Cc: Dave Taht <dave.taht@...il.com>, Jakub Kicinski <kuba@...nel.org>,
	"David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	almasrymina@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 0/4] Add support to do threaded napi busy poll

On Wed, Feb 05, 2025 at 09:49:04PM -0800, Samiullah Khawaja wrote:
> On Wed, Feb 5, 2025 at 9:36 PM Dave Taht <dave.taht@...il.com> wrote:
> >
> > I have often wondered the effects of reducing napi poll weight from 64
> > to 16 or less.
> Yes, that is Interesting. I think higher weight would allow it to
> fetch more descriptors doing more batching but then packets are pushed
> up the stack late. A lower value would push packet up the stack
> quicker, but then if the core is being shared with the application
> processing thread then the descriptors will spend more time in the NIC
> queue.

Seems testable?

> >
> > Also your test shows an increase in max latency...
> >
> > latency_max=0.200182942
> I noticed this anomaly and my guess is that it is a packet drop and
> this is basically a retransmit timeout. Going through tcpdumps to
> confirm.

Can you call out anomalies like this more explicitly and explain why
they occur?

If it weren't for Dave's response, I would have missed this.