On Thu, Apr 30, 2020 at 5:40 AM Václav Zindulka
[off-list ref] wrote:

On Wed, Apr 15, 2020 at 5:01 PM Václav Zindulka
[off-list ref] wrote:

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The problem is actually more complicated than I thought, although it
needs more work, below is the first pile of patches I have for you to
test:

https://github.com/congwang/linux/commits/qdisc_reset

It is based on the latest net-next branch. Please let me know the result.

I have applied all the patches in your four commits to my custom 5.4.6
kernel source. There was no change in the amount of fq_codel_reset
calls. Tested on ifb, RJ45 and SFP+ interfaces.

It is true my patches do not reduce the number of fq_codel_reset() calls,
they are intended to reduce the CPU time spent in each fq_codel_reset().

Can you measure this? Note, you do not have to add your own printk()
any more, because my patches add a few tracepoints, especially for
qdisc_reset(). So you can obtain the time by checking the timestamps
of these trace events. Of course, you can also use perf trace like you
did before.

Sorry for delayed responses. We were moving to a new house so I didn't
have much time to test it. I've measured your pile of patches applied
vs unpatched kernel. Result is a little bit better, but it is only
about 1s faster. Results are here. Do you need any additional reports
or measurements of other interfaces?
https://github.com/zvalcav/tc-kernel/tree/master/20200415 I've
recompiled the kernel without printk which had some overhead too.

Hello Cong,

did you have any time to look at it further? I'm just asking since my
boss wants me to give him some verdict. I've started to study eBPF and
XDP in the meantime so we have an alternative in case there won't be a
solution to this problem.

Sorry for the delay. I lost connection to my dev machine, I am trying
to setup this on my own laptop.

Regarding to your test result above, I think I saw some difference
on my side, I have no idea why you didn't see any difference. Please
let me collect the data once I setup the test environment shortly today.

Thanks!