Messages in this thread | | | Date | Sat, 13 Aug 2016 10:42:47 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] time,virt: resync steal time when guest & host lose sync |
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* Rik van Riel <riel@redhat.com> wrote:
> On Wed, 10 Aug 2016 07:39:08 +0800 > Wanpeng Li <kernellwp@gmail.com> wrote: > > > The regression is caused by your commit "sched,time: Count actually > > elapsed irq & softirq time". > > Wanpeng, does this patch fix your issue? > > Paolo, what is your opinion on this issue? > > I can think of all kinds of ways in which guest and host might lose > sync with steal time, from uninitialized values at boot, to guest > pause, followed by save to disk, and reload, to live migration, to... > > ---8<--- > > Subject: time,virt: resync steal time when guest & host lose sync > > When guest and host wildly disagree on steal time, a guest can > do several things: > 1) Quickly account all the steal time at once (the kernel did this before > 57430218317e ("sched/cputime: Count actually elapsed irq & softirq time"), > when steal_account_process_ticks got ULONG_MAX as its maximum value. > 2) Stay out of sync for an indeterminate amount of time. This is what the > system does today. > 3) Sync up the guest value to the host-provided value, without accounting > an absurdly large value in the cpu time statistics. > > This patch makes the kernel do (3), which seems like the right thing > to do. > > The exact value of the threshold use probably does not matter too much, > as long as it is long enough to cover all the timer ticks that passed > during an idle period, because (irqtime_)account_idle_ticks can process > a large amount of time all at once. > > Signed-off-by: Rik van Riel <riel@redhat.com> > Reported-by: Wanpeng Li <kernellwp@gmail.com> > --- > kernel/sched/cputime.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-)
fails to build on x86 allnoconfig:
kernel/sched/cputime.c:524:10: error: too many arguments to function ‘steal_account_process_time’
Thanks,
Ingo
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