| Message ID | 20150612140845.GD2749@TopQuark.net |
|---|---|
| State | New |
| Headers | show |
On 12/06/2015 16:08, Paul Donohue wrote: > +static inline int64_t get_max_clock_jump(void) > +{ > + // This should be small enough to prevent excessive interrupts from being > + // generated by the RTC on clock jumps, but large enough to avoid frequent > + // unnecessary resets in idle VMs. This is not how comments are layed out in QEMU... > + return 60 * get_ticks_per_sec(); > +} > + > /* > * * Low level clock functions > * */ ... and it also looks like your editor has mangled this patch. Nevertheless, I've applied it to my local branch and will send it out for inclusion after some more testing. Paolo > diff --git a/qemu-timer.c b/qemu-timer.c > index 5741f0d..d27be3d 100644 > --- a/qemu-timer.c > +++ b/qemu-timer.c
On Wed, Jun 17, 2015 at 04:00:06PM +0200, Paolo Bonzini wrote: > On 12/06/2015 16:08, Paul Donohue wrote: > > +static inline int64_t get_max_clock_jump(void) > > +{ > > + // This should be small enough to prevent excessive interrupts from being > > + // generated by the RTC on clock jumps, but large enough to avoid frequent > > + // unnecessary resets in idle VMs. > This is not how comments are layed out in QEMU... Oops. Sorry, I'm not sure how I missed that. Force of habit from other projects, I guess... > > + return 60 * get_ticks_per_sec(); > > +} > > + > > /* > > * * Low level clock functions > > * */ > ... and it also looks like your editor has mangled this patch. Ugh, yes. I do remember noticing that, and I thought I fixed it, but apparently not. I will correct and send an updated patch.
On 18/06/2015 14:58, Paul Donohue wrote: > On Wed, Jun 17, 2015 at 04:00:06PM +0200, Paolo Bonzini wrote: >> On 12/06/2015 16:08, Paul Donohue wrote: >>> +static inline int64_t get_max_clock_jump(void) >>> +{ >>> + // This should be small enough to prevent excessive interrupts from being >>> + // generated by the RTC on clock jumps, but large enough to avoid frequent >>> + // unnecessary resets in idle VMs. >> This is not how comments are layed out in QEMU... > Oops. Sorry, I'm not sure how I missed that. Force of habit from > other projects, I guess... > >>> + return 60 * get_ticks_per_sec(); >>> +} >>> + >>> /* >>> * * Low level clock functions >>> * */ >> ... and it also looks like your editor has mangled this patch. > Ugh, yes. I do remember noticing that, and I thought I fixed it, but > apparently not. > > I will correct and send an updated patch. No problem, I fixed this already. Paolo
diff --git a/include/qemu/timer.h b/include/qemu/timer.h index e5bd494..0193036 100644 --- a/include/qemu/timer.h +++ b/include/qemu/timer.h @@ -787,6 +787,14 @@ static inline int64_t get_ticks_per_sec(void) return 1000000000LL; } +static inline int64_t get_max_clock_jump(void) +{ + // This should be small enough to prevent excessive interrupts from being + // generated by the RTC on clock jumps, but large enough to avoid frequent + // unnecessary resets in idle VMs. + return 60 * get_ticks_per_sec(); +} + /* * * Low level clock functions * */ diff --git a/qemu-timer.c b/qemu-timer.c index 5741f0d..d27be3d 100644 --- a/qemu-timer.c +++ b/qemu-timer.c @@ -573,7 +573,7 @@ int64_t qemu_clock_get_ns(QEMUClockType type) now = get_clock_realtime(); last = clock->last; clock->last = now; - if (now < last) { + if (now < last || now > (last + get_max_clock_jump())) { notifier_list_notify(&clock->reset_notifiers, &now); } return now;
Commit 691a0c9c introduced a mechanism by which QEMU_CLOCK_HOST can notify other parts of the emulator when the host clock has jumped backward. This is used to avoid stalling timers that were scheduled based on the host clock. However, if the host clock jumps forward, then timers that were scheduled based on the host clock may fire rapidly and cause other problems. For example, the mc146818rtc periodic timer will block execution of the VM and consume host CPU while firing every interrupt for the time period that was skipped by the host clock. To correct that problem, this commit fires the reset notification if the host clock jumps forward by more than a hard-coded limit. The limit is currently set to a value of 60 seconds, which should be small enough to prevent excessive timer loops, but large enough to avoid frequent resets in idle VMs. Signed-off-by: Paul Donohue <qemu-git@PaulSD.com> --- include/qemu/timer.h | 9 +++++++++ qemu-timer.c | 2 +- 2 files changed, 10 insertions(+), 1 deletion(-)