On Thu, Apr 23, 2015 at 05:12:42PM -0400, Luiz Capitulino wrote: > If you try to enable NOHZ_FULL on a guest today, you'll get > the following error when the guest tries to deactivate the > scheduler tick: > > WARNING: CPU: 3 PID: 2182 at kernel/time/tick-sched.c:192 > can_stop_full_tick+0xb9/0x290() > NO_HZ FULL will not work with unstable sched clock > CPU: 3 PID: 2182 Comm: kworker/3:1 Not tainted 4.0.0-10545-gb9bb6fb #204 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 > Workqueue: events flush_to_ldisc > ffffffff8162a0c7 ffff88011f583e88 ffffffff814e6ba0 0000000000000002 > ffff88011f583ed8 ffff88011f583ec8 ffffffff8104d095 ffff88011f583eb8 > 0000000000000000 0000000000000003 0000000000000001 0000000000000001 > Call Trace: > <IRQ> [<ffffffff814e6ba0>] dump_stack+0x4f/0x7b > [<ffffffff8104d095>] warn_slowpath_common+0x85/0xc0 > [<ffffffff8104d146>] warn_slowpath_fmt+0x46/0x50 > [<ffffffff810bd2a9>] can_stop_full_tick+0xb9/0x290 > [<ffffffff810bd9ed>] tick_nohz_irq_exit+0x8d/0xb0 > [<ffffffff810511c5>] irq_exit+0xc5/0x130 > [<ffffffff814f180a>] smp_apic_timer_interrupt+0x4a/0x60 > [<ffffffff814eff5e>] apic_timer_interrupt+0x6e/0x80 > <EOI> [<ffffffff814ee5d1>] ? _raw_spin_unlock_irqrestore+0x31/0x60 > [<ffffffff8108bbc8>] __wake_up+0x48/0x60 > [<ffffffff8134836c>] n_tty_receive_buf_common+0x49c/0xba0 > [<ffffffff8134a6bf>] ? tty_ldisc_ref+0x1f/0x70 > [<ffffffff81348a84>] n_tty_receive_buf2+0x14/0x20 > [<ffffffff8134b390>] flush_to_ldisc+0xe0/0x120 > [<ffffffff81064d05>] process_one_work+0x1d5/0x540 > [<ffffffff81064c81>] ? process_one_work+0x151/0x540 > [<ffffffff81065191>] worker_thread+0x121/0x470 > [<ffffffff81065070>] ? process_one_work+0x540/0x540 > [<ffffffff8106b4df>] kthread+0xef/0x110 > [<ffffffff8106b3f0>] ? __kthread_parkme+0xa0/0xa0 > [<ffffffff814ef4f2>] ret_from_fork+0x42/0x70 > [<ffffffff8106b3f0>] ? __kthread_parkme+0xa0/0xa0 > ---[ end trace 06e3507544a38866 ]--- > > However, it turns out that kvmclock does provide a stable > sched_clock callback. So, let the scheduler know this which > in turn makes NOHZ_FULL work in the guest. > > Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com> > Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com> > --- > > PS: Original author of this patch is Marcelo. I did most of the > testing and backported it to an older real-time kernel tree. Works > like a charm. > > arch/x86/kernel/kvmclock.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c > index 42caaef..4e03921 100644 > --- a/arch/x86/kernel/kvmclock.c > +++ b/arch/x86/kernel/kvmclock.c > @@ -24,6 +24,7 @@ > #include <linux/percpu.h> > #include <linux/hardirq.h> > #include <linux/memblock.h> > +#include <linux/sched.h> > > #include <asm/x86_init.h> > #include <asm/reboot.h> > @@ -265,6 +266,8 @@ void __init kvmclock_init(void) > > if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT)) > pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT); > + > + set_sched_clock_stable(); > } > > int __init kvm_setup_vsyscall_timeinfo(void) > -- > 1.9.3 > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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