netdev - Re: [PATCH net-next 0/4] net: rps/rfs improvements

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Date:   Thu, 30 Mar 2023 05:39:35 +0200
From:   Eric Dumazet <edumazet@...gle.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Paolo Abeni <pabeni@...hat.com>,
        Jason Xing <kernelxing@...cent.com>, netdev@...r.kernel.org,
        eric.dumazet@...il.com
Subject: Re: [PATCH net-next 0/4] net: rps/rfs improvements

On Thu, Mar 30, 2023 at 5:15 AM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Thu, Mar 30, 2023 at 5:04 AM Jakub Kicinski <kuba@...nel.org> wrote:
> >
> > On Tue, 28 Mar 2023 23:50:17 +0000 Eric Dumazet wrote:
> > > Overall, in an intensive RPC workload, with 32 TX/RX queues with RFS
> > > I was able to observe a ~10% reduction of NET_RX_SOFTIRQ
> > > invocations.
> >
> > small clarification on the testing:
> >
> > invocations == calls to net_rx_action()
> > or
> > invocations == calls to __raise_softirq_irqoff(NET_RX_SOFTIRQ)
>
> This was from "grep NET_RX /proc/softirqs" (more exactly a tool
> parsing /proc/softirqs)
>
> So it should match the number of calls to net_rx_action(), but I can
> double check if you want.
>
> (I had a simple hack to enable/disable the optimizations with a hijacked sysctl)

Trace of real debug session, because numbers ;)
Old platform with two Intel(R) Xeon(R) Gold 6268L CPU @ 2.80GHz  (96
threads total)

600 tcp_rr flows

iroa23:/home/edumazet# cat /proc/sys/net/core/netdev_max_backlog
1000
iroa23:/home/edumazet# ./interrupts
hrtimer:99518 cal:2421783 timer:1034 sched:80505 rcu:7661 rps:2390765
net_tx:43 net_rx:3344637 eth1-rx:295134 eth1-tx:558933 eth1:854074
^C
iroa23:/home/edumazet# echo 1001 >/proc/sys/net/core/netdev_max_backlog
iroa23:/home/edumazet# ./interrupts
hrtimer:99545 cal:2358993 timer:1086 sched:77806 rcu:10928 rps:2419052
net_tx:21 net_rx:3016301 eth1-rx:294612 eth1-tx:560331 eth1:855083
^C

echo "(3344637 - 3016301)/3344637" | bc -ql
.09816790282473105452

-> ~10 % decrease.