Messages in this thread | | | Date | Fri, 8 Jul 2016 16:01:41 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 4/4] irqtime: drop local_irq_save/restore from irqtime_account_irq |
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On Fri, Jul 08, 2016 at 09:19:47AM -0400, Rik van Riel wrote: > On Fri, 2016-07-08 at 14:30 +0200, Frederic Weisbecker wrote: > > > + 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. > > Where does it break? > > enter hardirq A -> hardirq_start_time = now > > enter hardirq B -> hardirq_start_time = now, > account already elapsed time > > leave hardirq B -> account elapsed time, set > hardirq_start_time = now > > leave hardirq A -> account elapsed time > > What am I missing, except a softirq-style do-while > loop to account for hardirq A being interrupted by > hardirq B while updating the statistics?
How about:
enter hardirq A -> delta = sched_clock_cpu(cpu) - __this_cpu_read(hardirq_start_time); enter hardirq B -> delta = sched_clock_cpu(cpu) - __this_cpu_read(hardirq_start_time); __this_cpu_add(hardirq_start_time, delta); ... exit hardirq B __this_cpu_add(hardirq_start_time, delta);
Also seqcount writers can't nest.
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