On Tue, 2016-05-10 at 14:31 -0700, Eric Dumazet wrote:
> On Tue, 2016-05-10 at 14:09 -0700, Eric Dumazet wrote:
> >
> > On Tue, May 10, 2016 at 1:46 PM, Hannes Frederic Sowa
> > <han...@stressinduktion.org> wrote:
> >
> > >
> > > I agree here, but I don't think this patch particularly is a lot
> > > of
> > > bloat and something very interesting people can play with and
> > > extend upon.
> > >
> > Sure, very rarely patch authors think their stuff is bloat.
> >
> > I prefer to fix kernel softirq.c, or at least show me that you
> > tried
> > hard enough.
> >
> > I am pretty sure that the following would work :
> >
> > When ksoftirqd is scheduled, remember this in a per cpu variable
> > (ksoftiqd_scheduled)
> >
> > When enabling BH , do not call do_softirq() if this variable is
> > set.
> >
> > ksoftirqd would clear the variable at the right place (probably in
> > run_ksoftirqd())
> >
> > Sure, this might add a lot of latency regressions, but lets fix
> > them.
> Only to give the idea (it is completely untested and probably buggy)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 17caf4b63342..cb30cfd76687 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -56,6 +56,7 @@ EXPORT_SYMBOL(irq_stat);
> static struct softirq_action softirq_vec[NR_SOFTIRQS]
> __cacheline_aligned_in_smp;
>
> DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
> +DEFINE_PER_CPU(bool, ksoftirqd_scheduled);
>
> const char * const softirq_to_name[NR_SOFTIRQS] = {
> "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
> @@ -73,8 +74,10 @@ static void wakeup_softirqd(void)
> /* Interrupts are disabled: no need to stop preemption */
> struct task_struct *tsk = __this_cpu_read(ksoftirqd);
>
> - if (tsk && tsk->state != TASK_RUNNING)
> + if (tsk && tsk->state != TASK_RUNNING) {
> + __this_cpu_write(ksoftirqd_scheduled, true);
> wake_up_process(tsk);
> + }
> }
>
> /*
> @@ -162,7 +165,9 @@ void __local_bh_enable_ip(unsigned long ip,
> unsigned int cnt)
> */
> preempt_count_sub(cnt - 1);
>
> - if (unlikely(!in_interrupt() && local_softirq_pending())) {
> + if (unlikely(!in_interrupt() &&
> + local_softirq_pending() &&
> + !__this_cpu_read(ksoftirqd_scheduled))) {
> /*
> You might need another one of these in invoke_softirq() -- All Rights Reversed.
signature.asc
Description: This is a digitally signed message part
