From 0ad83caa21bff9f383c10e73b452425709573042 Mon Sep 17 00:00:00 2001 From: Luiz Capitulino Date: Thu, 28 May 2015 20:20:40 -0300 Subject: [PATCH] x86: kvmclock: set scheduler clock stable 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: [] dump_stack+0x4f/0x7b [] warn_slowpath_common+0x85/0xc0 [] warn_slowpath_fmt+0x46/0x50 [] can_stop_full_tick+0xb9/0x290 [] tick_nohz_irq_exit+0x8d/0xb0 [] irq_exit+0xc5/0x130 [] smp_apic_timer_interrupt+0x4a/0x60 [] apic_timer_interrupt+0x6e/0x80 [] ? _raw_spin_unlock_irqrestore+0x31/0x60 [] __wake_up+0x48/0x60 [] n_tty_receive_buf_common+0x49c/0xba0 [] ? tty_ldisc_ref+0x1f/0x70 [] n_tty_receive_buf2+0x14/0x20 [] flush_to_ldisc+0xe0/0x120 [] process_one_work+0x1d5/0x540 [] ? process_one_work+0x151/0x540 [] worker_thread+0x121/0x470 [] ? process_one_work+0x540/0x540 [] kthread+0xef/0x110 [] ? __kthread_parkme+0xa0/0xa0 [] ret_from_fork+0x42/0x70 [] ? __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 Signed-off-by: Luiz Capitulino Signed-off-by: Paolo Bonzini --- arch/x86/kernel/kvmclock.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c index 42caaef897c8..49487b488061 100644 --- a/arch/x86/kernel/kvmclock.c +++ b/arch/x86/kernel/kvmclock.c @@ -24,6 +24,7 @@ #include #include #include +#include #include #include @@ -217,8 +218,10 @@ static void kvm_shutdown(void) void __init kvmclock_init(void) { + struct pvclock_vcpu_time_info *vcpu_time; unsigned long mem; - int size; + int size, cpu; + u8 flags; size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS); @@ -264,7 +267,14 @@ void __init kvmclock_init(void) pv_info.name = "KVM"; if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT)) - pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT); + pvclock_set_flags(~0); + + cpu = get_cpu(); + vcpu_time = &hv_clock[cpu].pvti; + flags = pvclock_read_flags(vcpu_time); + if (flags & PVCLOCK_COUNTS_FROM_ZERO) + set_sched_clock_stable(); + put_cpu(); } int __init kvm_setup_vsyscall_timeinfo(void) -- 2.11.0