Re: [Xen-devel] Sched_op hypercall small questions

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

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.

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                         |
> >> +-------------------------------------+
> >>
> >>
> >>
> >
> >
> >
> 
> 
> 



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