On Mon, 11 Aug 2014 09:17:19 +0100 "Daniel P. Berrange" <berra...@redhat.com> wrote:
> On Wed, Jul 23, 2014 at 09:17:17AM -0400, Luiz Capitulino wrote: > > This event has the same characteristics of the other rate-limited > > events, mainly we can emit dozens of it. Rate limit it then. > > > > Signed-off-by: Luiz Capitulino <lcapitul...@redhat.com> > > --- > > monitor.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/monitor.c b/monitor.c > > index 5bc70a6..33abe6c 100644 > > --- a/monitor.c > > +++ b/monitor.c > > @@ -589,6 +589,7 @@ static void monitor_qapi_event_init(void) > > monitor_qapi_event_throttle(QAPI_EVENT_QUORUM_REPORT_BAD, 1000); > > monitor_qapi_event_throttle(QAPI_EVENT_QUORUM_FAILURE, 1000); > > monitor_qapi_event_throttle(QAPI_EVENT_VSERPORT_CHANGE, 1000); > > + monitor_qapi_event_throttle(QAPI_EVENT_BLOCK_IO_ERROR, 1000); > > > The rate limiting code only rate limits at the granularity of > individual event types. If there is context sensitive data associated > with events then the rate limiting will cause problems for applications > tracking the events. > > eg consider with the simpler RTC CHANGE events if we get > > QAPI_EVENT_RTC_CHANGE offset=30 > QAPI_EVENT_RTC_CHANGE offset=700 > QAPI_EVENT_RTC_CHANGE offset=340 > > then rate limiting will mean that the application only receives > > QAPI_EVENT_RTC_CHANGE offset=340 > > This is fine because the application will always end up with a correct > view of the current system state. > > > For the BLOCK IO ERROR events this does not work because the events are > device and operation specific. > > QAPI_EVENT_BLOCK_IO_ERROR dev=ide0-hd1 op=read action=stop > QAPI_EVENT_BLOCK_IO_ERROR dev=scsi1-hd2 op=write action=stop > QAPI_EVENT_BLOCK_IO_ERROR dev=ide0-hd1 op=write action=stop > > with throttling the app wll only receive > > QAPI_EVENT_BLOCK_IO_ERROR dev=ide0-hd1 op=write action=stop > > which means it will have an *incorrect* view of the system state because > the info about scsi1-hd2 is irretrievably lost, likewise info about the > read operation of ide0-hd1. You're completely right, of course. Thanks for reviewing! I think I'll just drop this patch for now. > > If you want to throttle BLOCK IO ERROR events, then you need to make the > monitor throttling more intelligent, so that it hashes on all the contextual > state. In this case you'd have to throttle based on (event, dev, op) to get > correct application behaviour. > > Regards, > Daniel
