netdev - Re: [PATCH net-next v1 5/6] ptp: Support late timestamp determination

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Date:   Thu, 24 Mar 2022 20:52:18 +0100
From:   Gerhard Engleder <gerhard@...leder-embedded.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     yangbo.lu@....com, David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, mlichvar@...hat.com,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v1 5/6] ptp: Support late timestamp determination

> > diff --git a/drivers/ptp/ptp_clock.c b/drivers/ptp/ptp_clock.c
> > index 54b9f54ac0b2..b7a8cf27c349 100644
> > --- a/drivers/ptp/ptp_clock.c
> > +++ b/drivers/ptp/ptp_clock.c
> > @@ -450,6 +450,33 @@ void ptp_cancel_worker_sync(struct ptp_clock *ptp)
> >  }
> >  EXPORT_SYMBOL(ptp_cancel_worker_sync);
> >
> > +ktime_t ptp_get_timestamp(int index,
> > +                       const struct skb_shared_hwtstamps *hwtstamps,
> > +                       bool cycles)
> > +{
> > +     char name[PTP_CLOCK_NAME_LEN] = "";
> > +     struct ptp_clock *ptp;
> > +     struct device *dev;
> > +     ktime_t ts;
> > +
> > +     snprintf(name, PTP_CLOCK_NAME_LEN, "ptp%d", index);
> > +     dev = class_find_device_by_name(ptp_class, name);
>
> This seems expensive for every single Rx frame in a busy PTP network.
> Can't this be cached in the socket?

I thought that PTP packages are rare and that bloating the socket is
not welcome.
I'll try to implement some caching.

> > --- a/include/linux/skbuff.h
> > +++ b/include/linux/skbuff.h
> > @@ -564,7 +564,10 @@ static inline bool skb_frag_must_loop(struct page *p)
> >   * &skb_shared_info. Use skb_hwtstamps() to get a pointer.
> >   */
> >  struct skb_shared_hwtstamps {
> > -     ktime_t hwtstamp;
> > +     union {
> > +             ktime_t hwtstamp;
> > +             void *phc_data;
>
> needs kdoc update

Sorry, I totally forgot that. I'll fix it.

> > @@ -886,18 +885,32 @@ void __sock_recv_timestamp(struct msghdr *msg, struct sock *sk,
> >       if (shhwtstamps &&
> >           (sk->sk_tsflags & SOF_TIMESTAMPING_RAW_HARDWARE) &&
> >           !skb_is_swtx_tstamp(skb, false_tstamp)) {
> > -             if (sk->sk_tsflags & SOF_TIMESTAMPING_BIND_PHC)
> > -                     hwtstamp = ptp_convert_timestamp(&shhwtstamps->hwtstamp,
> > -                                                      sk->sk_bind_phc);
> > +             rcu_read_lock();
> > +             orig_dev = dev_get_by_napi_id(skb_napi_id(skb));
> > +             if (orig_dev) {
> > +                     if_index = orig_dev->ifindex;
> > +                     if (skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP_PHC)
> > +                             phc_index = ethtool_get_phc(orig_dev);
>
> again, this is something that can be cached, no?

I'll try to implement some caching.

Thanks for your review!

Gerhard