Re: [net] 4890b686f4: netperf.Throughput_Mbps -69.4% regression

[Eric Dumazet]

On Mon, Jun 27, 2022 at 4:53 PM Shakeel Butt <shakeelb@xxxxxxxxxx> wrote:

> Am I understanding correctly that this 69.4% (or 73.7%) regression is
> with cgroup v2?
>
> Eric did the experiments on v2 but on real hardware where the
> performance impact was negligible.
>
> BTW do you see similar regression for tcp as well or just sctp?

TCP_RR with big packets can show a regression as well.

I gave this perf profile:

    28.69%  [kernel]       [k] copy_user_enhanced_fast_string
    16.13%  [kernel]       [k] intel_idle_irq
     6.46%  [kernel]       [k] page_counter_try_charge
     6.20%  [kernel]       [k] __sk_mem_reduce_allocated
     5.68%  [kernel]       [k] try_charge_memcg
     5.16%  [kernel]       [k] page_counter_cancel

And this points to false sharing on (struct page_counter *)->usage

I guess memcg had free lunch, because of per-socket cache, that we
need to remove.