Re: [PATCH net-next] net: introduce budget_squeeze to help us tune rx behavior

[Jason Xing]

On Tue, Mar 14, 2023 at 4:07 AM Simon Horman <simon.horman@xxxxxxxxxxxx> wrote:
>
> On Mon, Mar 13, 2023 at 10:05:18AM +0800, Jason Xing wrote:
> > On Sun, Mar 12, 2023 at 12:36 AM Jason Xing <kerneljasonxing@xxxxxxxxx> wrote:
> > >
> > > From: Jason Xing <kernelxing@xxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxx>
> > > ---
> > > note: this commit is based on the link as below:
> > > https://lore.kernel.org/lkml/20230311151756.83302-1-kerneljasonxing@xxxxxxxxx/
> > > ---
> > >  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..bed7a68fdb5d 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 is_continue = true;
> >
> > I kept thinking during these days, I think it looks not that concise
> > and elegant and also the name is not that good though the function can
> > work.
> >
> > In the next submission, I'm going to choose to use 'while()' instead
> > of 'for()' suggested by Stephen.
> >
> > Does anyone else have some advice about this?
>
> What about:
>
>         int done = false
>
>         while (!done) {
>                 ...
>         }
>
> Or:
>
>         for (;;) {
>                 int done = false;
>
>                 ...
>                 if (done)
>                         break;
>         }
>

Great, that looks much better:)

Thanks,
Jason

> >
> > Thanks,
> > Jason
> >
> > >         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 (;;) {
> > > +       for (; is_continue;) {
> > >                 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++;
> > > +                       is_continue = false;
> > > +               }
> > > +               if (unlikely(time_after_eq(jiffies, time_limit))) {
> > >                         sd->time_squeeze++;
> > > -                       break;
> > > +                       is_continue = false;
> > >                 }
> > >         }
> > >
> > > diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
> > > index 97a304e1957a..4d1a499d7c43 100644
> > > --- a/net/core/net-procfs.c
> > > +++ b/net/core/net-procfs.c
> > > @@ -174,14 +174,17 @@ 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,
> > > +                  0, /* was old way to count time squeeze */
> > > +                  0,
> > >                    0, 0, 0, 0, /* was fastroute */
> > >                    0,   /* was cpu_collision */
> > >                    sd->received_rps, flow_limit_count,
> > >                    0,   /* was len of two backlog queues */
> > >                    (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
> > >
> >