Messages in this thread | | | Subject | Re: [RFC PATCH 2/4] x86: Add IRQ_TIME_ACCOUNTING, finer accounting of irq time to task | From | Peter Zijlstra <> | Date | Tue, 25 May 2010 08:35:11 +0200 |
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On Mon, 2010-05-24 at 17:11 -0700, Venkatesh Pallipadi wrote: > +void account_system_vtime(struct task_struct *tsk) > +{ > + unsigned long flags; > + int cpu; > + u64 now; > + > + local_irq_save(flags); > + cpu = task_cpu(tsk); > + now = sched_clock_cpu(cpu); > + if (hardirq_count()) > + tsk->hi_time += now - per_cpu(irq_start_time, cpu); > + else if (softirq_count()) > + tsk->si_time += now - per_cpu(irq_start_time, cpu); > + > + per_cpu(irq_start_time, cpu) = now; > + local_irq_restore(flags); > +}
Right, so this gets called from irq_enter/exit() and __do_softirq().
The reason I never pressed onwards with this (I had patches to add IRQ time accounting) is that it sucks terribly for anything falling back to jiffies -- maybe find some smart way to disable the whole call when there's no TSC available, preferably without adding conditionals, using alternatives maybe?
I guess you mostly side-stepped that by adding a IRQ_TIME_ACCOUNTING config (but forgot to make it depend on X86_TSC).
Another thing I dislike about this account_system_vtime() is that its the same call for both IRQ and SoftIRQ, leaving us to add conditionals inside the call to figure out what context we got called from.
[ Adedd the s390 and ppc guys who already use this stuff ]
Anyway, once we have this, please also add it to sched_rt_avg_update() (which should really be called sched_!fair_avg_update()).
Also, did you measure the overhead of doing this? sched_clock_cpu() adds a cmpxchg64 on all systems that don't have a rock solid TSC (ie. most of todays machines).
Another thing that would be real nice is if you could find a way to not make all of this x86 specific.
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