netdev - Re: XDP Performance Regression in recent kernel versions

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Message-ID: <CA+h3auPydMVmWRKPKQJ75Gg5c8uhttVik4seCtmPXduQxQSjMQ@mail.gmail.com>
Date: Wed, 11 Dec 2024 14:20:14 +0100
From: Samuel Dobron <sdobron@...hat.com>
To: Carolina Jubran <cjubran@...dia.com>, Dragos Tatulea <dtatulea@...dia.com>, 
	Tariq Toukan <tariqt@...dia.com>, "daniel@...earbox.net" <daniel@...earbox.net>, 
	"hawk@...nel.org" <hawk@...nel.org>, "mianosebastiano@...il.com" <mianosebastiano@...il.com>
Cc: "toke@...hat.com" <toke@...hat.com>, "pabeni@...hat.com" <pabeni@...hat.com>, 
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>, "edumazet@...gle.com" <edumazet@...gle.com>, 
	Saeed Mahameed <saeedm@...dia.com>, "bpf@...r.kernel.org" <bpf@...r.kernel.org>, 
	"kuba@...nel.org" <kuba@...nel.org>, Benjamin Poirier <bpoirier@...hat.com>
Subject: Re: XDP Performance Regression in recent kernel versions

Hey all,

We recently enabled tests for XDP TX, so I was able to test
xdp tx as well.

XDP_DROP performance regression is the same as I reported
a while ago. There is about 20% regression in
kernel-6.4.0-0.rc6.20230616git40f71e7cd3c6.50.eln126 (baseline)
compared to previous kernel
kernel-6.4.0-0.rc6.20230614gitb6dad5178cea.49.eln126 (broken).
We don't see such regression for other drivers.

The regression was partially fixed somewhere between eln126 and
kernel-6.10.0-0.rc2.20240606git2df0193e62cf.27.eln137 (partially
fixed) and the performance since then is -7 to -15% compared to
baseline. So, nothing new.

XDP_TX is however, more interesting.
When comparing baseline with broken kernel there is 20 - 25%
performance drop (cpu utilizations remains the same) on mlx driver.
There is also 10% drop on other drivers as well. HOWEVER, it got
fixed somewhere between broken and partially fixed kernel. On most
recent kernels, we don't see that regressions on other drivers. But
2-10% (depends if using dpa/load-bytes) regression remains on mlx5.

The numbers look a bit similar to regression with enabled spectre/meltdown
mitigations but based on my experiments, there is no difference with
enabled/disabled mitigations.

Hope this will help,
Sam.

On Tue, Jul 30, 2024 at 1:04 PM Samuel Dobron <sdobron@...hat.com> wrote:
>
> > Could you try adding the mentioned parameters to your kernel arguments
> > and check if you still see the degradation?
>
> Hey,
> So i tried multiple kernels around v5.15 as well as couple of previous
> v6.xx and there is no difference with spectre v2 mitigations enabled
> or disabled.
>
> No difference on other drivers as well.
>
>
> Sam.
>