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Re: [Xen-devel] Sched_op hypercall small questions

On Tue, Sep 20, 2011 at 2:41 PM, Keir Fraser <keir.xen@xxxxxxxxx> wrote:
> On 19/09/2011 22:21, "Daniel Castro" <evil.dani@xxxxxxxxx> wrote:
>> Greetings all.
>> Some small question regarding schedule poll operation hypercall.
>> 1. struct sched_poll poll.timeout is measured in what unit of time?
>> Secs, ms? ns?
> It is an absolute system time (rather than a duration), in nanoseconds.

really an absolute system time?

When the timeout is set and the timeout is reached, the system behaves
like if the event had been received? i.e the bit is changed?

>> 2. After issuing the hypercall_sched_op(SCHEDOP_poll, &poll); if no
>> timeout is used in poll struct how long will I yield the CPU?
> Until one of the specified event channel ports is pending.
If the channel port never changes (the event never arrives) then I
would yield for ever?
>> 3. If I issue the hypercall and the event never comes is it possible
>> to to yield the CPU for ever?
> Yes, if you do not specify a timeout.

Keir thanks for the answer.

I am trying to read from xenstore, so I have the following:
I write on my xenstore ring the query I want, then,
hypercall_event_channel_op(EVTCHNOP_send ...
If I read the ring inmediatly the answer is not ready so I issue a
hypercall_sched_op(SCHEDOP_poll, &poll);
But while I am entering the yield state the answer comes, so the event
is never seen because it has already been delivered.

If I use some way to wait (just for very brief instant) after the
event_channel_op send then, when I check the ring the answer is there;
And I do not need to yield the CPU.

Should I issue the wait after the send, rather than when I am about to
read the answer?


>  -- Keir
>> Thanks you very much for answering these questions.
>> Daniel Castro

| +---------------------------------+ | This space intentionally blank
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| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
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