Re: [PATCH 4/9] softirq: Allow early break

[liujian (CE)]

On 2023/5/5 20:10, Eric Dumazet wrote:
> On Fri, May 5, 2023 at 1:24 PM Liu Jian <liujian56@xxxxxxxxxx> wrote:
> > From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> >
> > Allow terminating the softirq processing loop without finishing the
> > vectors.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx>
> > ---
> >   kernel/softirq.c | 16 ++++++++++------
> >   1 file changed, 10 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/softirq.c b/kernel/softirq.c
> > index 48a81d8ae49a..e2cad5d108c8 100644
> > --- a/kernel/softirq.c
> > +++ b/kernel/softirq.c
> > @@ -582,6 +582,9 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
> >                                 prev_count, preempt_count());
> >                          preempt_count_set(prev_count);
> >                  }
> > +
> > +               if (pending && __softirq_needs_break(start))
> > +                       break;
>
> This means that some softirq may starve, because
>
> for_each_set_bit(vec_nr, &pending, NR_SOFTIRQS)
>
> Always iterate using the same order (of bits)
Yes, we need to record the softirq that is not executed and continue 
next time. I will fix it in next version.
Thanks.
> >          }
> >
> >          if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
> > @@ -590,13 +593,14 @@ asmlinkage __visible void __softirq_entry __do_softirq(void)
> >
> >          local_irq_disable();
> >
> > -       pending = local_softirq_pending();
> > -       if (pending) {
> > -               if (!__softirq_needs_break(start) && --max_restart)
> > -                       goto restart;
> > +       if (pending)
> > +               or_softirq_pending(pending);
> > +       else if ((pending = local_softirq_pending()) &&
> > +                !__softirq_needs_break(start) &&
> > +                --max_restart)
> > +               goto restart;
> >
> > -               wakeup_softirqd();
> > -       }
> > +       wakeup_softirqd();
> >
> >          account_softirq_exit(current);
> >          lockdep_softirq_end(in_hardirq);
> > --
> > 2.34.1