Re: [patch 2/3] pvclock: detect watchdog reset at pvclock read

Don Zickus
2013-10-08T13:37:05Z

On Mon, Oct 07, 2013 at 10:05:17PM -0300, Marcelo Tosatti wrote:
> Implement reset of kernel watchdogs at pvclock read time. This avoids
> adding special code to every watchdog.
>
> This is possible for watchdogs which measure time based on sched_clock() or
> ktime_get() variants.
>
> Suggested by Don Zickus.
>
> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Awesome. Thanks for figuring this out Marcelo. Does that mean we can
revert commit 5d1c0f4a now? :-)

This meets my expectations. I'll leave it to the virt folks to figure out
if this covers all the corner cases or not.

Cheers,
Don

>
> Index: kvm/arch/x86/kernel/kvmclock.c
> ===================================================================
> --- kvm.orig/arch/x86/kernel/kvmclock.c
> +++ kvm/arch/x86/kernel/kvmclock.c
> @@ -139,6 +139,7 @@ bool kvm_check_and_clear_guest_paused(vo
> src = &hv_clock[cpu].pvti;
> if ((src->flags & PVCLOCK_GUEST_STOPPED) != 0) {
> src->flags &= ~PVCLOCK_GUEST_STOPPED;
> + pvclock_touch_watchdogs();
> ret = true;
> }
>
> Index: kvm/arch/x86/kernel/pvclock.c
> ===================================================================
> --- kvm.orig/arch/x86/kernel/pvclock.c
> +++ kvm/arch/x86/kernel/pvclock.c
> @@ -21,6 +21,7 @@
> #include <linux/sched.h>
> #include <linux/gfp.h>
> #include <linux/bootmem.h>
> +#include <linux/hung_task.h>
> #include <asm/fixmap.h>
> #include <asm/pvclock.h>
>
> @@ -43,6 +44,14 @@ unsigned long pvclock_tsc_khz(struct pvc
> return pv_tsc_khz;
> }
>
> +void pvclock_touch_watchdogs(void)
> +{
> + touch_softlockup_watchdog_sync();
> + clocksource_touch_watchdog();
> + rcu_cpu_stall_reset();
> + reset_hung_task_detector();
> +}
> +
> static atomic64_t last_value = ATOMIC64_INIT(0);
>
> void pvclock_resume(void)
> @@ -74,6 +83,11 @@ cycle_t pvclock_clocksource_read(struct
> version = __pvclock_read_cycles(src, &ret, &flags);
> } while ((src->version & 1) || version != src->version);
>
> + if (unlikely((flags & PVCLOCK_GUEST_STOPPED) != 0)) {
> + src->flags &= ~PVCLOCK_GUEST_STOPPED;
> + pvclock_touch_watchdogs();
> + }
> +
> if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
> (flags & PVCLOCK_TSC_STABLE_BIT))
> return ret;
> Index: kvm/arch/x86/include/asm/pvclock.h
> ===================================================================
> --- kvm.orig/arch/x86/include/asm/pvclock.h
> +++ kvm/arch/x86/include/asm/pvclock.h
> @@ -14,6 +14,8 @@ void pvclock_read_wallclock(struct pvclo
> struct timespec *ts);
> void pvclock_resume(void);
>
> +void pvclock_touch_watchdogs(void);
> +
> /*
> * Scale a 64-bit delta by scaling and multiplying by a 32-bit fraction,
> * yielding a 64-bit result.
>
>