netdev - Re: [PATCH net-next 2/3] bpf: add TCP_BPF_RTO_MAX for bpf

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Message-ID: <CAL+tcoApvV0vyiTKdaMWMp8F=ZWSodUg0zD+eq_F6kp=oh=hmA@mail.gmail.com>
Date: Fri, 14 Feb 2025 14:12:49 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Stanislav Fomichev <stfomichev@...il.com>, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, pabeni@...hat.com, dsahern@...nel.org, ast@...nel.org, 
	daniel@...earbox.net, andrii@...nel.org, eddyz87@...il.com, song@...nel.org, 
	yonghong.song@...ux.dev, john.fastabend@...il.com, kpsingh@...nel.org, 
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, horms@...nel.org, 
	ncardwell@...gle.com, kuniyu@...zon.com, bpf@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH net-next 2/3] bpf: add TCP_BPF_RTO_MAX for bpf_setsockopt

On Fri, Feb 14, 2025 at 1:41 PM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> On 2/13/25 7:09 PM, Jason Xing wrote:
> > On Fri, Feb 14, 2025 at 10:14 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
> >>
> >> On 2/13/25 3:57 PM, Jason Xing wrote:
> >>> On Fri, Feb 14, 2025 at 7:41 AM Stanislav Fomichev<stfomichev@...il.com> wrote:
> >>>> On 02/13, Jason Xing wrote:
> >>>>> Support bpf_setsockopt() to set the maximum value of RTO for
> >>>>> BPF program.
> >>>>>
> >>>>> Signed-off-by: Jason Xing<kerneljasonxing@...il.com>
> >>>>> ---
> >>>>>    Documentation/networking/ip-sysctl.rst | 3 ++-
> >>>>>    include/uapi/linux/bpf.h               | 2 ++
> >>>>>    net/core/filter.c                      | 6 ++++++
> >>>>>    tools/include/uapi/linux/bpf.h         | 2 ++
> >>>>>    4 files changed, 12 insertions(+), 1 deletion(-)
> >>>>>
> >>>>> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> >>>>> index 054561f8dcae..78eb0959438a 100644
> >>>>> --- a/Documentation/networking/ip-sysctl.rst
> >>>>> +++ b/Documentation/networking/ip-sysctl.rst
> >>>>> @@ -1241,7 +1241,8 @@ tcp_rto_min_us - INTEGER
> >>>>>
> >>>>>    tcp_rto_max_ms - INTEGER
> >>>>>         Maximal TCP retransmission timeout (in ms).
> >>>>> -     Note that TCP_RTO_MAX_MS socket option has higher precedence.
> >>>>> +     Note that TCP_BPF_RTO_MAX and TCP_RTO_MAX_MS socket option have the
> >>>>> +     higher precedence for configuring this setting.
> >>>> The cover letter needs more explanation about the motivation.
> >>
> >> +1
> >>
> >> I haven't looked at the patches. The cover letter has no word on the use case.
>
> The question was your _use case_ in bpf. Not what the TCP_RTO_MAX_MS does. Your
> current use case is to have bpf setting it after reading the tcp header option,
> like the selftest in patch 3?

Oops, I misunderstood the real situation of the tcp header option
test. My intention is to bpf_setsockopt() just like setget_sockopt
does.

Thanks for reminding me. I will totally remove the header test in the
next version.

>
> >
> > I will add and copy some words from Eric's patch series :)
>
>
> >>> I am targeting the net-next tree because of recent changes[1] made by
> >>> Eric. It probably hasn't merged into the bpf-next tree.
> >>
> >> There is the bpf-next/net tree. It should have the needed changes.
> >
> > [1] was recently merged in the net-next tree, so the only one branch I
> > can target is net-next.
> >
> > [1]: https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=ae9b3c0e79bc
> >
> > Am I missing something?
>
> There is a net branch:
> https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git

But this branch hasn't included the rto max feature. I was trying to
say that what I wrote is based on the rto max feature which only
exists in the net-next tree for now.

I wonder whether I need to introduce a new flag like this patch or
reuse the TCP_RTO_MAX_MS socket option for bpf?

Thanks,
Jason