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

[Simon Horman <simon.horman@corigine.com>]

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@gmail.com> wrote:
> >
> > From: Jason Xing <kernelxing@tencent.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@tencent.com>
> > ---
> > note: this commit is based on the link as below:
> > https://lore.kernel.org/lkml/20230311151756.83302-1-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..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;
	}

> 
> 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
> >
>