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

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Message-ID: <CAL+tcoAdYO_NnkWLYbxxRgw0=muhM0TJo3FBEeCBYtBmsnfWUw@mail.gmail.com>
Date:   Tue, 21 Feb 2023 21:44:25 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Paolo Abeni <pabeni@...hat.com>, willemdebruijn.kernel@...il.com,
        davem@...emloft.net, dsahern@...nel.org, 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 8:35 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Tue, Feb 21, 2023 at 1:27 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?
> >
> > Thanks!
> >
> > Paolo
> >
>
> Probably not a big deal.
>

> TCP skb truesize can easily reach 180 KB, but for UDP it's 99% below
> or close to a 4K page.

Yes.

>
> I doubt this change makes any difference for UDP.

Based on my understanding of this part, it could not neither cause
much regression nor improve much performance. I think what you've done
to the TCP stack is the right way to go so the UDP can probably follow
this.
Calculating extra memory is a little bit odd because we actually don't
need that much when receiving skb everytime.

Thanks,
Jason