netdev - Re: [PATCH net-next 2/2] vsock/virtio: avoid enqueue packets when work queue is empty

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Date: Tue, 18 Jun 2024 19:05:54 +0200
From: Luigi Leonardi <luigi.leonardi@...look.com>
To: mvaralar@...hat.com
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kuba@...nel.org,
	kvm@...r.kernel.org,
	luigi.leonardi@...look.com,
	marco.pinn95@...il.com,
	netdev@...r.kernel.org,
	pabeni@...hat.com,
	sgarzare@...hat.com,
	stefanha@...hat.com,
	virtualization@...ts.linux.dev
Subject: Re: [PATCH net-next 2/2] vsock/virtio: avoid enqueue packets when work queue is empty

Hi Stefano and Matias,

@Stefano Thanks for your review(s)! I'll send a V2 by the end of the week.

@Matias

Thanks for your feedback!

> I think It would be interesting to know what exactly the test does

It's relatively easy: I used fio's pingpong mode. This mode is specifically
for measuring the latency, the way it works is by sending packets,
in my case, from the host to the guest. and waiting for the other side
to send them back. The latency I wrote in the commit is the "completion
latency". The total throughput on my system is around 16 Gb/sec.

> if the test is triggering the improvement

Yes! I did some additional testing and I can confirm you that during this
test, the worker queue is never used!

> If I understand correctly, this patch focuses on the
> case in which the worker queue is empty

Correct!

> I think the test can always send packets at a frequency so the worker queue
> is always empty. but maybe, this is a corner case and most of the time the
> worker queue is not empty in a non-testing environment.

I'm not sure about this, but IMHO this optimization is free, there is no
penalty for using it, in the worst case the system will work as usual.
In any case, I'm more than happy to do some additional testing, do you have
anything in mind?

Luigi