Message-ID: <66d9c45f8b419_18de4129492@willemb.c.googlers.com.notmuch>
Date: Thu, 05 Sep 2024 10:46:55 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Jason Xing <kerneljasonxing@...il.com>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: davem@...emloft.net, 
 edumazet@...gle.com, 
 kuba@...nel.org, 
 pabeni@...hat.com, 
 dsahern@...nel.org, 
 shuah@...nel.org, 
 willemb@...gle.com, 
 linux-kselftest@...r.kernel.org, 
 netdev@...r.kernel.org, 
 Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4 3/4] net-timestamp: extend
 SOF_TIMESTAMPING_OPT_RX_FILTER for hardware use

Jason Xing wrote:
> On Thu, Sep 5, 2024 at 9:45 PM Willem de Bruijn
> <willemdebruijn.kernel@...il.com> wrote:
> >
> > Jason Xing wrote:
> > > From: Jason Xing <kernelxing@...cent.com>
> > >
> > > In the previous patch, we found things could happen in the rx software
> > > timestamp. Here, we also noticed that, for rx hardware timestamp case,
> > > it could happen when one process enables the rx hardware timestamp
> > > generating flag first, then another process only setting
> > > SOF_TIMESTAMPING_RAW_HARDWARE report flag can still get the hardware
> > > timestamp.
> > >
> > > In this patch, we extend the OPT_RX_FILTER flag to filter out the
> > > above case for hardware use.
> > >
> > > Suggested-by: Jakub Kicinski <kuba@...nel.org>
> > > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > > ---
> > > Link: https://lore.kernel.org/all/20240903121940.6390b958@kernel.org/
> > > ---
> > >  Documentation/networking/timestamping.rst | 15 +++++++++------
> > >  net/core/sock.c                           |  5 +++--
> > >  net/ipv4/tcp.c                            |  3 ++-
> > >  net/socket.c                              |  3 ++-
> > >  4 files changed, 16 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
> > > index ac57d9de2f11..55e79ea71f3e 100644
> > > --- a/Documentation/networking/timestamping.rst
> > > +++ b/Documentation/networking/timestamping.rst
> > > @@ -268,12 +268,15 @@ SOF_TIMESTAMPING_OPT_TX_SWHW:
> > >    each containing just one timestamp.
> > >
> > >  SOF_TIMESTAMPING_OPT_RX_FILTER:
> > > -  Used in the receive software timestamp. Enabling the flag along with
> > > -  SOF_TIMESTAMPING_SOFTWARE will not report the rx timestamp to the
> > > -  userspace so that it can filter out the case where one process starts
> > > -  first which turns on netstamp_needed_key through setting generation
> > > -  flags like SOF_TIMESTAMPING_RX_SOFTWARE, then another one only passing
> > > -  SOF_TIMESTAMPING_SOFTWARE report flag could also get the rx timestamp.
> > > +  Used in the receive software/hardware timestamp. Enabling the flag
> > > +  along with SOF_TIMESTAMPING_SOFTWARE/SOF_TIMESTAMPING_RAW_HARDWARE
> > > +  will not report the rx timestamp to the userspace so that it can
> > > +  filter out the cases where 1) one process starts first which turns
> > > +  on netstamp_needed_key through setting generation flags like
> > > +  SOF_TIMESTAMPING_RX_SOFTWARE, or 2) similarly one process enables
> > > +  generating the hardware timestamp already, then another one only
> > > +  passing SOF_TIMESTAMPING_SOFTWARE report flag could also get the
> > > +  rx timestamp.
> >
> > I think this patch should be squashed into patch 1.
> >
> > Else SOF_TIMESTAMPING_OPT_RX_FILTER has two subtly different behaviors
> > across its lifetime. Even if it is only two SHA1s apart.
> 
> I thought about last night as well. Like the patch [2/4] and this
> patch, the reason why I wanted to split is because I have to explain a
> lot for both hw and sw in one patch. One patch mixes different things.
> 
> No strong preference. If you still think so, I definitely can squash
> them as you said :)

No strong preference on 2/4. See other reply.

In this case, patch 1/4 introduces some behavior and 3/4 immediately
updates it. I think it makes more sense to combine them.

> >
> > It also avoids such duplicate changes to the same code/text blocks.
> >
> > More importantly, it matters for the behavior, see below.
> >
> > >
> > >    SOF_TIMESTAMPING_OPT_RX_FILTER prevents the application from being
> > >    influenced by others and let the application choose whether to report
> > > diff --git a/net/core/sock.c b/net/core/sock.c
> > > index 6a93344e21cf..dc4a43cfff59 100644
> > > --- a/net/core/sock.c
> > > +++ b/net/core/sock.c
> > > @@ -908,8 +908,9 @@ int sock_set_timestamping(struct sock *sk, int optname,
> > >           !(val & SOF_TIMESTAMPING_OPT_ID))
> > >               return -EINVAL;
> > >
> > > -     if (val & SOF_TIMESTAMPING_RX_SOFTWARE &&
> > > -         val & SOF_TIMESTAMPING_OPT_RX_FILTER)
> > > +     if (val & SOF_TIMESTAMPING_OPT_RX_FILTER &&
> > > +         (val & SOF_TIMESTAMPING_RX_SOFTWARE ||
> > > +          val & SOF_TIMESTAMPING_RX_HARDWARE))
> > >               return -EINVAL;
> >
> > There may be legitimate use cases of wanting to receive hardware
> > receive timestamps, plus software transmit timestamp, but
> > suppress spurious software timestamps (or vice versa):
> >
> >     SOF_TIMESTAMPING_RAW_HARDWARE | \
> >     SOF_TIMESTAMPING_RX_HARDWARE | \
> >     SOF_TIMESTAMPING_SOFTWARE | \
> >     SOF_TIMESTAMPING_TX_SOFTWARE | \
> >     SOF_TIMESTAMPING_OPT_RX_FILTER
> 
> Oh, right, it can happen! RAW_HARDWARE is a little bit different,
> covering both ingress and egress path.

As said, it is a bit contrived. Feel free to disagree and keep as is
too.
 
> >
> > Admittedly this seems a bit contrived. But it's little hassle to
> > support it?
> >
> > We just can no longer use the branch simplification that Jakub
> > pointed out.
> >
> 
> I see. I'm going to do two things as you said:
> 1) restore the simplification branch
> 2) only take care of software case in sock_set_timestamping()
> 
> Thanks for pointing this out!

Powered by blists - more mailing lists