From: Jason Xing <kerneljasonxing@gmail.com>
To: Paolo Abeni <pabeni@redhat.com>
Cc: davem@davemloft.net, edumazet@google.com, kuba@kernel.org,
matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org,
mptcp@lists.linux.dev, netdev@vger.kernel.org,
Jason Xing <kernelxing@tencent.com>
Subject: Re: [PATCH net-next 1/2] mptcp: don't need to check SKB_EXT_MPTCP in mptcp_reset_option()
Date: Fri, 5 Apr 2024 17:11:05 +0800 [thread overview]
Message-ID: <CAL+tcoBFS9Z-=H5g8hoyDVuvcmT+wEuAdT6GxyS-vh0hKdE8cw@mail.gmail.com> (raw)
In-Reply-To: <6b77ce4f71dae82a0be793cf17fac4fda0884501.camel@redhat.com>
Hello Paolo,
On Fri, Apr 5, 2024 at 4:34 PM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Fri, 2024-04-05 at 15:58 +0800, Jason Xing wrote:
> > Hello Paolo,
> >
> > On Fri, Apr 5, 2024 at 3:47 PM Paolo Abeni <pabeni@redhat.com> wrote:
> > >
> > > On Fri, 2024-04-05 at 10:39 +0800, Jason Xing wrote:
> > > > From: Jason Xing <kernelxing@tencent.com>
> > > >
> > > > Before this, what mptcp_reset_option() checks is totally the same as
> > > > mptcp_get_ext() does, so we could skip it.
> > >
> > > Note that the somewhat duplicate test is (a possibly not great)
> > > optimization to avoid jumping in the mptcp code (possible icache
> > > misses) for plain TCP sockets.
> > >
> > > I guess we want to maintain it.
> >
> > Okay, I just read code and found the duplication but may I ask why it
> > has something to do with icache misses?
>
> The first check/mptcp_get_ext() is in mptcp_reset_option() /
> tcp_v4_send_reset(). For plain TCP socket it will fail and the
> execution will continue inside the same compilation unit. The code
> locality should avoid icaches misses around there.
>
> Removing such check, even when processing plain TCP packets, the code
> execution will have to call into mptcp_get_reset_option() in the mptcp
> code, decreasing the code locality and increasing the chance of icache
> misses.
Interesting. Thanks for the explanation:)
>
> I don't have actual profile data, so this is an early optimization (and
> thus root of all evil), but sounds reasonable to me (yep, I'm biased!)
I'll drop this patch.
Thanks,
Jason
>
> Cheers,
>
> Paolo
>
next prev parent reply other threads:[~2024-04-05 9:11 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-05 2:39 [PATCH net-next 0/2] mptcp: add reset reasons in skb in more cases Jason Xing
2024-04-05 2:39 ` [PATCH net-next 1/2] mptcp: don't need to check SKB_EXT_MPTCP in mptcp_reset_option() Jason Xing
2024-04-05 7:47 ` Paolo Abeni
2024-04-05 7:58 ` Jason Xing
2024-04-05 8:34 ` Paolo Abeni
2024-04-05 9:11 ` Jason Xing [this message]
2024-04-05 2:39 ` [PATCH net-next 2/2] mptcp: add reset reason options in some places Jason Xing
2024-04-05 8:16 ` Paolo Abeni
2024-04-05 9:09 ` Jason Xing
2024-04-05 3:27 ` [PATCH net-next 0/2] mptcp: add reset reasons in skb in more cases MPTCP CI
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