Re: [Xen-devel] Sched_op hypercall small questions

[Daniel Castro <evil.dani@xxxxxxxxx>]

On Thu, Sep 22, 2011 at 5:00 PM, Ian Campbell
<Ian.Campbell@xxxxxxxxxxxxx> wrote:
> On Thu, 2011-09-22 at 08:43 +0100, Daniel Castro wrote:
>> On Thu, Sep 22, 2011 at 3:30 PM, Ian Campbell <Ian.Campbell@xxxxxxxxxx> 
>> wrote:
>
>> Thanks for the answer Ian, one question: If I do not manually change
>> the mask bit, then after writing to the ring and the response arrives
>> how can I be sure that xenstore is delivering an event?
>
> Add some printfs in the daemon?
>
>> I am suspecting that xenstore does not use event notification for simple
>> read and write operations. Could I be right?
>
> I don't think so, how else would it notify the client end that it should
> look into the ring?
>
> In the daemon the do_read() function calls the same common send_reply()
> as most (all?) other commands. send_reply queues a message on
> conn->out_list. Later on write_messages() dequeues it and calls the
> connections write method, which is writechn() in this case (the other
> case is a local socket connection which uses writefd but isn't relevant
> here). writechn() has an xc_evtchn_notify() at the end.

You are right as usual, using trace in the deamon in function writechn I get:
DEBUG notify dom 1 on port 42
Form /usr/lib/xen/bin/lsevtchn I get:
42: VCPU 0: Interdomain (Connected) - Remote Domain 1, Port 2
And from the guest I have:
Event is interdomain to dom 0 port 42

So they are interconected and the xenstore deamon is delivering the event.

I am going to check the ring waiting function there has to be
something I am missing....

thanks,
Daniel
>
> Ian.
>
>>
>> >
>> >>
>> >> Thanks
>> >> >
>> >> >>>> 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.
>> >> >
>> >> > It generally only makes sense to poll on masked events.
>> >> >
>> >> >>
>> >> >> 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?
>> >> >
>> >> > What environment is this in?
>> >> >
>> >> >    J
>> >> >
>> >>
>> >>
>> >>
>> >> --
>> >> +-=====---------------------------+
>> >> | +---------------------------------+ | This space intentionally blank
>> >> for notetaking.
>> >> | |   | Daniel Castro,                |
>> >> | |   | Consultant/Programmer.|
>> >> | |   | U Andes                         |
>> >> +-------------------------------------+
>> >>
>> >>
>> >>
>> >
>> >
>> >
>>
>>
>>
>
>
>



-- 
+-=====---------------------------+
| +---------------------------------+ | This space intentionally blank
for notetaking.
| |   | Daniel Castro,                |
| |   | Consultant/Programmer.|
| |   | U Andes                         |
+-------------------------------------+

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