linux-kernel - Re: [PATCH net-next] net-sysfs: display two backlog queue len separately

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Date:   Mon, 13 Mar 2023 21:15:27 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next] net-sysfs: display two backlog queue len separately

On Mon, Mar 13, 2023 at 8:34 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Sat, Mar 11, 2023 at 7:18 AM Jason Xing <kerneljasonxing@...il.com> wrote:
> >
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > Sometimes we need to know which one of backlog queue can be exactly
> > long enough to cause some latency when debugging this part is needed.
> > Thus, we can then separate the display of both.
> >
> > Signed-off-by: Jason Xing <kernelxing@...cent.com>
> > ---
> >  net/core/net-procfs.c | 17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
> > index 1ec23bf8b05c..97a304e1957a 100644
> > --- a/net/core/net-procfs.c
> > +++ b/net/core/net-procfs.c
> > @@ -115,10 +115,14 @@ static int dev_seq_show(struct seq_file *seq, void *v)
> >         return 0;
> >  }
> >
> > -static u32 softnet_backlog_len(struct softnet_data *sd)
> > +static u32 softnet_input_pkt_queue_len(struct softnet_data *sd)
> >  {
> > -       return skb_queue_len_lockless(&sd->input_pkt_queue) +
> > -              skb_queue_len_lockless(&sd->process_queue);
> > +       return skb_queue_len_lockless(&sd->input_pkt_queue);
> > +}
> > +
> > +static u32 softnet_process_queue_len(struct softnet_data *sd)
> > +{
> > +       return skb_queue_len_lockless(&sd->process_queue);
> >  }
> >
> >  static struct softnet_data *softnet_get_online(loff_t *pos)
> > @@ -169,12 +173,15 @@ static int softnet_seq_show(struct seq_file *seq, void *v)
> >          * mapping the data a specific CPU
> >          */
> >         seq_printf(seq,
> > -                  "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
> > +                  "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x "
> > +                  "%08x %08x\n",
> >                    sd->processed, sd->dropped, sd->time_squeeze, 0,
> >                    0, 0, 0, 0, /* was fastroute */
> >                    0,   /* was cpu_collision */
> >                    sd->received_rps, flow_limit_count,
> > -                  softnet_backlog_len(sd), (int)seq->index);
> > +                  0,   /* was len of two backlog queues */
>
> You can not pretend the sum is zero, some user space tools out there
> would be fooled.
>
> > +                  (int)seq->index,
> > +                  softnet_input_pkt_queue_len(sd), softnet_process_queue_len(sd));
> >         return 0;
> >  }
> >
> > --
> > 2.37.3
> >
>
> In general I would prefer we no longer change this file.

Fine. Since now, let this legacy file be one part of history.

>
> Perhaps add a tracepoint instead ?

Thanks, Eric. It's one good idea. It seems acceptable if we only need
to trace two separate backlog queues where it can probably hit the
limit, say, in the enqueue_to_backlog().

Similarly I decide to write another two tracepoints of time_squeeze
and budget_squeeze which I introduced to distinguish from time_squeeze
as the below link shows:
https://lore.kernel.org/lkml/CAL+tcoAwodpnE2NjMLPhBbmHUvmKMgSykqx0EQ4YZaQHjrx0Hw@mail.gmail.com/.
For that change, any suggestions are deeply welcome :)

Thanks,
Jason