Re: [Xen-devel] linux: {start, stop}_hz_timer() not really affecting periodic timer?

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> The call to VCPUOP_set_singleshot_timer cannot return -ETIME because the
>>> kernel does not specify the VCPU_SSHOTTMR_future flag.
>> 
>> I noticed this after pushing the send button. Nevertheless, the whole
>> construct in stop_hz_timer() seems to assume that it is called with
>> interrupts disabled, which might be the case now but nothing enforces
>> xen_safe_halt() to only be called in such contexts... For that reason it
>> would seem safer to set the flag, check for -ETIME, and avoid
>> HYPERVISOR_block() altogether in that case.
>
>If the time is in the past then the singleshot timer will fire immediately.
>So you'll take a slower path than necessary, but the code as-is will work
>fine.

Immediately would mean to me that it would fire on the return path
from VCPUOP_set_singleshot_timer, so HYPERVISOR_block() would
not (necessarily) find any pending events and hence block when it
shouldn't. Or am I missing some magic by which this is being avoided?

Jan


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