Messages in this thread | | | Date | Fri, 8 Jul 2016 14:30:11 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 4/4] irqtime: drop local_irq_save/restore from irqtime_account_irq |
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On Thu, Jun 30, 2016 at 03:35:50PM -0400, riel@redhat.com wrote: > From: Rik van Riel <riel@redhat.com> > > Drop local_irq_save/restore from irqtime_account_irq. > Instead, have softirq and hardirq track their time spent > independently, with the softirq code subtracting hardirq > time that happened during the duration of the softirq run. > > The softirq code can be interrupted by hardirq code at > any point in time, but it can check whether it got a > consistent snapshot of the timekeeping variables it wants, > and loop around in the unlikely case that it did not. > > Signed-off-by: Rik van Riel <riel@redhat.com>
So the purpose is to get rid of local_irq_save/restore()? Is it really worth such complication?
> --- > kernel/sched/cputime.c | 72 +++++++++++++++++++++++++++++++++++++++++--------- > kernel/sched/sched.h | 38 +++++++++++++++++++++----- > 2 files changed, 90 insertions(+), 20 deletions(-) > > diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c > index a0aefd4c7ea6..b78991fac228 100644 > --- a/kernel/sched/cputime.c > +++ b/kernel/sched/cputime.c > @@ -26,7 +26,9 @@ > DEFINE_PER_CPU(u64, cpu_hardirq_time); > DEFINE_PER_CPU(u64, cpu_softirq_time); > > -static DEFINE_PER_CPU(u64, irq_start_time); > +static DEFINE_PER_CPU(u64, hardirq_start_time); > +static DEFINE_PER_CPU(u64, softirq_start_time); > +static DEFINE_PER_CPU(u64, prev_hardirq_time); > static int sched_clock_irqtime; > > void enable_sched_clock_irqtime(void) > @@ -41,6 +43,7 @@ void disable_sched_clock_irqtime(void) > > #ifndef CONFIG_64BIT > DEFINE_PER_CPU(seqcount_t, irq_time_seq); > +DEFINE_PER_CPU(seqcount_t, softirq_time_seq); > #endif /* CONFIG_64BIT */ > > /* > @@ -53,36 +56,79 @@ DEFINE_PER_CPU(seqcount_t, irq_time_seq); > * softirq -> hardirq, hardirq -> softirq > * > * When exiting hardirq or softirq time, account the elapsed time. > + * > + * When exiting softirq time, subtract the amount of hardirq time that > + * interrupted this softirq run, to avoid double accounting of that time. > */ > void irqtime_account_irq(struct task_struct *curr, int irqtype) > { > - unsigned long flags; > + u64 prev_softirq_start; > + bool leaving_softirq; > + u64 prev_hardirq; > + u64 hardirq_time; > s64 delta; > int cpu; > > if (!sched_clock_irqtime) > return; > > - local_irq_save(flags); > - > cpu = smp_processor_id(); > - delta = sched_clock_cpu(cpu) - __this_cpu_read(irq_start_time); > - __this_cpu_add(irq_start_time, delta); > > - irq_time_write_begin(); > + /* > + * Hardirq time accounting is pretty straightforward. If not in > + * hardirq context yet (entering hardirq), set the start time. > + * If already in hardirq context (leaving), account the elapsed time. > + */ > + if (irqtype == HARDIRQ_OFFSET) { > + bool leaving_hardirq = hardirq_count(); > + delta = sched_clock_cpu(cpu) - __this_cpu_read(hardirq_start_time); > + __this_cpu_add(hardirq_start_time, delta); > + if (leaving_hardirq) { > + hardirq_time_write_begin(); > + __this_cpu_add(cpu_hardirq_time, delta); > + hardirq_time_write_end(); > + }
This doesn't seem to work with nesting hardirqs.
Thanks.
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