tolerance

Set how much the host system is allowed to delay before notifying the hypervisor of a timer expiry

Synopsis:

tolerance microseconds

Option:

microseconds: The emulated timer device tolerance, in microseconds. Default is 10 percent of the timer tick period.

Description:

To support guest system virtualized timer hardware (e.g., the hpet vdev on x86), the hypervisor uses QNX host system timers to generate notifications when a guest timer interrupt needs to be delivered.

These QNX timer notifications aren't delivered to the hypervisor exactly at the requested point of timer expiry; there may be a delay between timer expiry and notification delivery. Since the guest's interrupts will be delivered later than it expects, this delay may cause inaccuracies in the virtualization of the guest.

The tolerance option sets the maximum allowed amount of time, specified in microseconds, that the host system is allowed to delay before notifying the hypervisor of a timer expiry. If the tolerance option isn't specified, the tolerance defaults to 10 percent of the host system clock period (which defaults to 1ms, making the default tolerance 100us).

CAUTION:

Setting a lower value for the tolerance will improve guest interrupt delivery latency, but it may also increase system load and thus decrease overall performance.