Messages in this thread | | | Date | Thu, 21 Jun 2012 02:46:29 +0200 | Subject | Re: [PATCH 0/4] cputime: Virtual cputime accounting small cleanups and consolidation | From | Frederic Weisbecker <> |
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2012/6/21 Peter Zijlstra <peterz@infradead.org>: > On Tue, 2012-06-19 at 15:43 +0200, Frederic Weisbecker wrote: >> >> I wish we could do more vtime cputime accounting consolidation >> but archs do the things pretty differently although I bet the >> behaviour could be more unified. >> > Yes.. so s390,ia64 use thread_info, ppc uses their paca (arch private > precursor to per-cpu data). > > So I understand why s390,ia64 want the sched hook, but I don't see why > ppc would need it, their account_process_tick() can fold whatever they > need on the tick.
I think in any case you need to flush the time on a descheduling task otherwise its pending time will be accounted later to the next task when it receives an irq.
So I fear we still need that sched switch hook even with per cpu data. This may be a simple account_system_vtime() call.
> So I think reworking s390,ia64 to use per-cpu storage should get rid of > this switch hook altogether. > > > Now everybody using VIRT_CPU_ACCOUNTING has the > syscall/__irq_{enter,exit} hooks and uses 64bit cputime_t. > > IRQ_TIME_ACCOUNTING only has the __irq_{enter,exit} hook and uses > unsigned long cputime_t, it adds cputime_one_jiffy every tick when the > per-cpu counter is ahead of the cputime. > > > We could merge both and do away with the 64bit cputime thing by keeping > a (2nd) per-cpu kernel_cpustat which we fill with optional syscall/irq > hooks and have account_process_tick() first check if any of the > fine-grained fields overflow and if not, fall back to the regular tick > accounting (much like an extended irqtime_account_process_tick). > > > This would merge the fine-grain and tick based code-paths and do away > with the whole cputime_t mess, it would also merge the VIRT and IRQ > paths and make Frederic's optional syscall accounting trivial. > > Or am I missing something obvious here? -- its late after all.
No that looks pretty sensible.
> I'll try and write some code tomorrow.
Thanks!
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