netdev - Re: [PATCH net] udp: fix memory schedule error

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Date:   Tue, 21 Feb 2023 21:39:00 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     willemdebruijn.kernel@...il.com, davem@...emloft.net,
        dsahern@...nel.org, edumazet@...gle.com, kuba@...nel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net] udp: fix memory schedule error

On Tue, Feb 21, 2023 at 8:27 PM Paolo Abeni <pabeni@...hat.com> wrote:
>
> On Tue, 2023-02-21 at 19:03 +0800, Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Quoting from the commit 7c80b038d23e ("net: fix sk_wmem_schedule()
> > and sk_rmem_schedule() errors"):
> >
> > "If sk->sk_forward_alloc is 150000, and we need to schedule 150001 bytes,
> > we want to allocate 1 byte more (rounded up to one page),
> > instead of 150001"
>
> I'm wondering if this would cause measurable (even small) performance
> regression? Specifically under high packet rate, with BH and user-space
> processing happening on different CPUs.
>
> Could you please provide the relevant performance figures?

Sure, I've done some basic tests on my machine as below.

Environment: 16 cpus, 60G memory
Server: run "iperf3 -s -p [port]" command and start 500 processes.
Client: run "iperf3 -u -c 127.0.0.1 -p [port]" command and start 500 processes.

Running such tests makes sure that the util output of every cpu is
higher than 15% which is observed through top command.

Here're some before/after numbers by using the "sar -n DEV 10 2" command.
Before: rxpck/s 2000, txpck/s 2000, rxkB/s 64054.69, txkB/s 64054.69
After: rxpck/s 2000, txpck/s 2000, rxkB/s 64054.58, txkB/s 64054.58
So I don't see much impact on the results.

In theory, I have no clue about why it could cause some regression?
Maybe the memory allocation is not that enough compared to the
original code?

Thanks,
Jason

>
> Thanks!
>
> Paolo
>