From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: Hypercall continuation and wait_event Date: Mon, 09 Apr 2012 21:09:19 +0100 Message-ID: References: <1333999130.48871.YahooMailNeo@web124501.mail.ne1.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1333999130.48871.YahooMailNeo@web124501.mail.ne1.yahoo.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Ruslan Nikolaev , "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On 09/04/2012 20:18, "Ruslan Nikolaev" wrote: > Thanks for the reply. > > Since it can take arbitrarily long for an event to arrive (e.g., it is coming > from a different guest on a user request), how do I need to handle this > case?Does it mean that I only need to make sure that nothings get scheduled on > this VCPU in the guest? Nothing else *can* get scheduled on this VCPU in the guest. The VCPU will sleep within wait_event within the hypercall context. Hence you must not hold any hypervisor spinlocks either, for example. > Also, it is not exactly clear to me how wait_event avoids the need for > hypercall continuation. What about local_events_need_delivery() or > softirq_pending()? Are they going to be handled by wait_event internally? Your VCPU gets descheduled. Hence softirq_pending() is not your concern for the duration that you're descheduled. And if local_event_need_delivery(), that's too bad, they have to wait for the vcpu to wake up on the event. -- Keir > Ruslan > > > > > > > ----- Original Message ----- > From: Keir Fraser > To: Ruslan Nikolaev ; "xen-devel@lists.xen.org" > > Cc: > Sent: Monday, April 9, 2012 6:54 PM > Subject: Re: [Xen-devel] Hypercall continuation and wait_event > > On 09/04/2012 18:51, "Ruslan Nikolaev" wrote: > >> Hi >> >> I am curious how I can properly support hypercall continuation and >> wait_event. >> I have a dedicated VCPU in a domain which makes a special hypercall, and the >> hypercall waits for certain event to arrive. I am using queues available in >> Xen, so wait_event will be invoked in the hypercall once its ready to accept >> events. However, my understanding that even though I have a dedicated VCPU >> for >> this hypercall, I still may need to support hypercall continuation properly. >> (Is this the case?) So, my question is how exactly the need for hypercall > > No it's not the case, the old hypercall_create_continuation() mechanism does > not need to be used with wait_event(). > > -- Keir > >> preemption may affect wait_event() and wait() operations, and where would I >> need to do hypercall_preempt_check()? >> >> Thank you! >> Ruslan >> >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xen.org >> http://lists.xen.org/xen-devel > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xen.org > http://lists.xen.org/xen-devel