Am Donnerstag, 15. November 2007 schrieb Laurent Vivier: > If I remember correctly time accounting on s390 is more accurate than on > x86 ?
Yes. its done during context switches and resolution is microsecond. > Because on x86, as we make the kvm_guest_exit() after local_irq_enable() > we can also have IRQ with PF_VCPU set... and we discussed a lot on > probability to know if it was good or not. And on x86 it seems good > because it is already working like that with system and user time (we > account time to the space where tick appears). > see http://lkml.org/lkml/2007/10/15/228 I am not sure I fully understand your point, can you try to explain? My patch deals with timer ticks (see hardirq_offset). So if a only a tick comes in after local_irq_enable the time is accounted to guest time as before. I made a test on x86_64 with burnP6 inside a kvm machine. top showed 100% guest time on an otherwise idle host. So the guest accounting itself did still work. I tried some disk and network stress on the host but I did not manage to bring hardirq+softirq time above 5%, guest time stayed above 90%. At least my simple testcase did not show a bias towards irq time. > Le jeudi 15 novembre 2007 à 15:10 +0100, Christian Borntraeger a écrit : > > Avi pointed out, that my first patch was broken, here is the 2nd try. > > I tested the patch on s390 with CONFIG_VIRT_CPU_ACCOUNTING and on x86_64. > > Seems to work. > > > > Currently the scheduler checks for PF_VCPU to decide if this > > timeslice has to be accounted as guest time. On s390 host > > interrupts are not disabled during guest execution. This causes > > theses interrupts to be accounted as guest time if > > CONFIG_VIRT_CPU_ACCOUNTING is set. > > Solution is to check if an interrupt triggered account_system_time. > > As the tick is timer interrupt based, we have to subtract > > hardirq_offset. > > > > Avi, Ingo, Laurent, feedback is welcome. > > > > CC: Ingo Molnar <[EMAIL PROTECTED]> > > CC: Avi Kivity <[EMAIL PROTECTED]> > > CC: Laurent Vivier <[EMAIL PROTECTED]> > > Signed-off-by: Christian Borntraeger <[EMAIL PROTECTED]> > > --- > > kernel/sched.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > Index: kvm/kernel/sched.c > > =================================================================== > > --- kvm.orig/kernel/sched.c > > +++ kvm/kernel/sched.c > > @@ -3395,10 +3395,8 @@ void account_system_time(struct task_str > > struct rq *rq = this_rq(); > > cputime64_t tmp; > > > > - if (p->flags & PF_VCPU) { > > - account_guest_time(p, cputime); > > - return; > > - } > > + if ((p->flags & PF_VCPU) && (irq_count() - hardirq_offset == 0)) > > + return account_guest_time(p, cputime); > > > > p->stime = cputime_add(p->stime, cputime); ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
