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 <20230314030532.9238-2-kerneljasonxing@gmail.com> <CANn89iKP7GVxZ0HYcPQq5ryC+rtwyymZuHuvza_SoCOJeADzGw@mail.gmail.com>
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From:   Jason Xing <kerneljasonxing@gmail.com>
Date:   Tue, 14 Mar 2023 23:44:21 +0800
Message-ID: <CAL+tcoANe4FMSCvTH46ToPqMsEUSwwKMhdT+z_hR7hEE0FsL7g@mail.gmail.com>
Subject: Re: [PATCH v2 net-next 1/2] net-sysfs: display two backlog queue len separately
To:     Eric Dumazet <edumazet@google.com>
Cc:     davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com,
        ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org,
        john.fastabend@gmail.com, stephen@networkplumber.org,
        simon.horman@corigine.com, sinquersw@gmail.com,
        bpf@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, Jason Xing <kernelxing@tencent.com>
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On Tue, Mar 14, 2023 at 10:59=E2=80=AFPM Eric Dumazet <edumazet@google.com>=
 wrote:
>
> On Mon, Mar 13, 2023 at 8:06=E2=80=AFPM Jason Xing <kerneljasonxing@gmail=
.com> wrote:
> >
> > From: Jason Xing <kernelxing@tencent.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@tencent.com>
> > ---
> > v2: keep the total len of backlog queues untouched as Eric said
> > Link: https://lore.kernel.org/lkml/20230311151756.83302-1-kerneljasonxi=
ng@gmail.com/
> > ---
> >  net/core/net-procfs.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
> > index 1ec23bf8b05c..2809b663e78d 100644
> > --- a/net/core/net-procfs.c
> > +++ b/net/core/net-procfs.c
> > @@ -115,10 +115,19 @@ static int dev_seq_show(struct seq_file *seq, voi=
d *v)
> >         return 0;
> >  }
> >
> > +static u32 softnet_input_pkt_queue_len(struct softnet_data *sd)
> > +{
> > +       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 u32 softnet_backlog_len(struct softnet_data *sd)
> >  {
> > -       return skb_queue_len_lockless(&sd->input_pkt_queue) +
> > -              skb_queue_len_lockless(&sd->process_queue);
> > +       return softnet_input_pkt_queue_len(sd) + softnet_process_queue_=
len(sd);
>
[...]
> Reading these variables twice might lead to inconsistency that can
> easily be avoided.
>
> I would suggest you cache the values,
>
> u32 len1 =3D softnet_input_pkt_queue_len(sd);
> u32 len2 =3D softnet_process_queue_len(sd);

Agreed. Thank you, Eric. I should have realized that.

Also, the 2/2 patch which is all about the time_/budget_squeeze should
avoid such inconsistency, I think.

Jason
>
>
>
> >  }
> >
> >  static struct softnet_data *softnet_get_online(loff_t *pos)
> > @@ -169,12 +178,15 @@ 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);
> > +                  softnet_backlog_len(sd),     /* keep it untouched */
>                     len1 + len2.
>
> > +                  (int)seq->index,
> > +                  softnet_input_pkt_queue_len(sd), softnet_process_que=
ue_len(sd));
>                len1,  len2);
>
> >         return 0;
> >  }
> >
> > --
> > 2.37.3
> >