Hello,
Thank you Sam for the detailed information.
I have identified the specific kernel configuration change responsible
for the degradation between kernel versions
6.4.0-0.rc6.20230614gitb6dad5178cea.49.eln126 and
6.4.0-0.rc6.20230616git40f71e7cd3c6.50.eln126. The introduction of the
CONFIG_INIT_STACK_ALL_ZERO setting in the latter version has led to a
noticeable performance impact.
I am currently investigating why this change specifically affects mlx5.
Thanks,
Carolina
On 11/12/2024 15:20, Samuel Dobron wrote:
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@xxxxxxxxxx> 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.
