Messages in this thread | | | Date | Tue, 20 Dec 2016 15:30:29 +0100 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 09/10] s390/cputime: delayed accounting of system time |
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On Tue, Dec 20, 2016 at 03:13:53PM +0100, Martin Schwidefsky wrote: > On Wed, 14 Dec 2016 02:44:46 +0100 > Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > On Tue, Dec 13, 2016 at 02:21:21PM +0100, Martin Schwidefsky wrote: > > > On Tue, 13 Dec 2016 12:13:22 +0100 > > > Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: > > > > > > > On Mon, 12 Dec 2016 16:02:30 +0100 > > > > Frederic Weisbecker <fweisbec@gmail.com> wrote: > > > > > > > > > On Mon, Dec 12, 2016 at 11:27:54AM +0100, Martin Schwidefsky wrote: > > > > > > 3) The call to vtime_flush in account_process_tick is done in irq context from > > > > > > update_process_times. hardirq_offset==1 is also correct. > > > > > > > > > > Let's see this for example: > > > > > > > > > > + if ((tsk->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) > > > > > + S390_lowcore.guest_timer += timer; > > > > > > > > > > If the tick is interrupting guest, we have accounted the guest time on tick IRQ entry. > > > > > Now we are in the middle of the tick interrupt and since hardirq_offset is 1, we > > > > > are taking the above path by accounting half of the tick-IRQ time as guest, which is wrong, > > > > > it's actually IRQ time. > > > > > > > > Hmm, you got me there. The system time from irq_enter until account_process_tick > > > > is reached is indeed IRQ time. It is not much but it is incorrect. The best fix > > > > would be to rip out the accounting of the system time from account_process_tick > > > > as irq_enter / irq_exit will do system time accounting anyway. To do that > > > > do_account_vtime needs to be split, because for the task switch we need to > > > > account the system time of the previous task. > > > > > > New patch for the delayed cputime account. I can not just rip out system time > > > accounting from account_process_tick after all, I need a sync point for the > > > steal time calculation. It basically is the same patch as before but with a new > > > helper update_tsk_timer, the removal of hardirq_offset and a simplification > > > for do_account_vtime: the last accounting delta is either hardirq time for > > > the tick or system time for the task switch. > > > > > > Keeping my finger crossed.. > > > > The patch looks good. But you might want to remove the hardirq_offset in a > > separate patch to queue for this merge window (I'm not sure if it needs a > > stable tag, the argument may be there since the beginning). > > > > Because the rest depends on the series that is unlikely to be queued in this > > merge window at this stage. > > I just pushed two fixes to the linux-s390:fixes tree which will be merged > eventually after the first -rc candidate for 4.10 is released. > > This includes "s390/vtime: correct system time accounting" which fixes the > hardirq_offset bug for s390. > > The link to the fixes-tree in case you want to look at the patch: > > git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git fixes
Thanks a lot!
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