From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Castro Subject: Sched_op hypercall small questions Date: Thu, 22 Sep 2011 14:41:20 +0900 Message-ID: References: <4E793DC4.7080808@goop.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On Wed, Sep 21, 2011 at 10:28 AM, Jeremy Fitzhardinge wro= te: > On 09/19/2011 11:17 PM, Daniel Castro wrote: >> On Tue, Sep 20, 2011 at 2:41 PM, Keir Fraser wrote: >>> On 19/09/2011 22:21, "Daniel Castro" 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? > > You specify the timeout in the the form "wake up by time t". =A0If t is i= n > the past, it times out immediately. > >>>> 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? > > If you have events unmasked and you get an unmasked event, then it will > go into the event handler. My vcpu[0].evntchn_upcall_mask is 0, does this prevents the guest from receiving events? would that also explain why poll hypercall returns immediately? According to Xen's Definitive Guide evntchn_upcall_mask is unset at boot (my case exactly) so if it is 0 from the start and the guest (me) has to change it to 1 in order to receive events. How can I change the flag, I tried changing the value but it does not work like that apparently. 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? > > =A0 =A0J > -- +-=3D=3D=3D=3D=3D---------------------------+ | +---------------------------------+ | This space intentionally blank for notetaking. | |=A0=A0 | Daniel Castro,=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | | |=A0=A0 | Consultant/Programmer.| | |=A0=A0 | U Andes=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=A0 | +-------------------------------------+ --=20 +-=3D=3D=3D=3D=3D---------------------------+ | +---------------------------------+ | This space intentionally blank for notetaking. | |=A0=A0 | Daniel Castro,=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | | |=A0=A0 | Consultant/Programmer.| | |=A0=A0 | U Andes=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0=A0 | +-------------------------------------+