netdev - Re: [PATCH net-next v4 3/4] net-timestamp: extend SOF_TIMESTAMPING_OPT_RX

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Message-ID: <CAL+tcoC9_sCunEzM6sLqWkhuZETYmAYxPWY-utenbDCWoUe6vg@mail.gmail.com>
Date: Fri, 6 Sep 2024 00:57:33 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: 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

On Fri, Sep 6, 2024 at 12:41 AM Willem de Bruijn
<willemdebruijn.kernel@...il.com> wrote:
>
> Jason Xing wrote:
> > On Thu, Sep 5, 2024 at 10:46 PM Willem de Bruijn
> > <willemdebruijn.kernel@...il.com> wrote:
> > >
> > > 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.
> >
> > Roger that. Will squash this one:)
> >
> > >
> > > > >
> > > > > 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
> >
> > Sorry, I think my initial understanding at first read is not right. I
> > was thinking you want this combination to pass the check in
> > sock_set_timestamping().
> >
> > If the users insist on receiving "hardware receive timestamps" with
> > OPT_RX_FILTER enabled in this case, I think we should implement
> > another new flag, say, OPT_RX_HARDWARE_FILTER...
>
> My interpretation of the OPT_RX_FILTER flag is:
>
> Only return RX timestamps if the socket also has the corresponding
> reporting flag set.
>
> So it is valid to have
>
>   SOF_TIMESTAMPING_RAW_HARDWARE |
>   SOF_TIMESTAMPING_RX_HARDWARE |
>   SOF_TIMESTAMPING_SOFTWARE |
>   SOF_TIMESTAMPING_OPT_RX_FILTER
>
> To filter out the software rx timestamps, but let through the
> hardware rx timestamps.

I see. Thanks for your advice.

If both SOF_TIMESTAMPING_RX_SOFTWARE and
SOF_TIMESTAMPING_OPT_RX_FILTER are set at once, the latter will not
take any effect.

I will 1) completely remove the limitation in sock_set_timestamping(),
2) restore those simplification branches.