linux-kernel - Re: [PATCH v2 net-next 2/2] net: introduce budget

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Date:   Tue, 14 Mar 2023 20:31:46 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net,
        hawk@...nel.org, john.fastabend@...il.com,
        stephen@...workplumber.org, sinquersw@...il.com,
        bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH v2 net-next 2/2] net: introduce budget_squeeze to help us
 tune rx behavior

On Tue, Mar 14, 2023 at 8:04 PM Simon Horman <simon.horman@...igine.com> wrote:
>
> On Tue, Mar 14, 2023 at 11:05:32AM +0800, Jason Xing wrote:
> > From: Jason Xing <kernelxing@...cent.com>
> >
> > When we encounter some performance issue and then get lost on how
> > to tune the budget limit and time limit in net_rx_action() function,
> > we can separately counting both of them to avoid the confusion.
> >
> > Signed-off-by: Jason Xing <kernelxing@...cent.com>
>
> As per my comment on patch 1/2, I'd drop the "/* keep it untouched */"
> comment.

I think you're right. I'll drop this.

Thanks,
Jason

>
> That notwithstanding:
>
> Reviewed-by: Simon Horman <simon.horman@...igine.com>
>
> > ---
> > v2:
> > 1) change the coding style suggested by Stephen and Simon
> > 2) Keep the display of the old data (time_squeeze) untouched suggested
> > by Kui-Feng
> > Link: https://lore.kernel.org/lkml/20230311163614.92296-1-kerneljasonxing@gmail.com/
> > ---
> >  include/linux/netdevice.h |  1 +
> >  net/core/dev.c            | 12 ++++++++----
> >  net/core/net-procfs.c     |  9 ++++++---
> >  3 files changed, 15 insertions(+), 7 deletions(-)
> >
> > diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> > index 6a14b7b11766..5736311a2133 100644
> > --- a/include/linux/netdevice.h
> > +++ b/include/linux/netdevice.h
> > @@ -3157,6 +3157,7 @@ struct softnet_data {
> >       /* stats */
> >       unsigned int            processed;
> >       unsigned int            time_squeeze;
> > +     unsigned int            budget_squeeze;
> >  #ifdef CONFIG_RPS
> >       struct softnet_data     *rps_ipi_list;
> >  #endif
> > diff --git a/net/core/dev.c b/net/core/dev.c
> > index 253584777101..1518a366783b 100644
> > --- a/net/core/dev.c
> > +++ b/net/core/dev.c
> > @@ -6637,6 +6637,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
> >       unsigned long time_limit = jiffies +
> >               usecs_to_jiffies(READ_ONCE(netdev_budget_usecs));
> >       int budget = READ_ONCE(netdev_budget);
> > +     bool done = false;
> >       LIST_HEAD(list);
> >       LIST_HEAD(repoll);
> >
> > @@ -6644,7 +6645,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
> >       list_splice_init(&sd->poll_list, &list);
> >       local_irq_enable();
> >
> > -     for (;;) {
> > +     while (!done) {
> >               struct napi_struct *n;
> >
> >               skb_defer_free_flush(sd);
> > @@ -6662,10 +6663,13 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
> >                * Allow this to run for 2 jiffies since which will allow
> >                * an average latency of 1.5/HZ.
> >                */
> > -             if (unlikely(budget <= 0 ||
> > -                          time_after_eq(jiffies, time_limit))) {
> > +             if (unlikely(budget <= 0)) {
> > +                     sd->budget_squeeze++;
> > +                     done = true;
> > +             }
> > +             if (unlikely(time_after_eq(jiffies, time_limit))) {
> >                       sd->time_squeeze++;
> > -                     break;
> > +                     done = true;
> >               }
> >       }
> >
> > diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
> > index 2809b663e78d..25810ee46a04 100644
> > --- a/net/core/net-procfs.c
> > +++ b/net/core/net-procfs.c
> > @@ -179,14 +179,17 @@ static int softnet_seq_show(struct seq_file *seq, void *v)
> >        */
> >       seq_printf(seq,
> >                  "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x "
> > -                "%08x %08x\n",
> > -                sd->processed, sd->dropped, sd->time_squeeze, 0,
> > +                "%08x %08x %08x %08x\n",
> > +                sd->processed, sd->dropped,
> > +                sd->time_squeeze + sd->budget_squeeze, /* keep it untouched */
> > +                0,
> >                  0, 0, 0, 0, /* was fastroute */
> >                  0,   /* was cpu_collision */
> >                  sd->received_rps, flow_limit_count,
> >                  softnet_backlog_len(sd),     /* keep it untouched */
> >                  (int)seq->index,
> > -                softnet_input_pkt_queue_len(sd), softnet_process_queue_len(sd));
> > +                softnet_input_pkt_queue_len(sd), softnet_process_queue_len(sd),
> > +                sd->time_squeeze, sd->budget_squeeze);
> >       return 0;
> >  }
> >
> > --
> > 2.37.3
> >