Re: [Xen-devel] mapped memory delay?

[Christopher Clark <christopher.clark@xxxxxxxxxxxx>]

This sounds like the symptoms you'd experience with multiple functions
using the same event channel port.

How are you obtaining the ports you're using to communicate?
Are you using alloc_unbound ?

c.

On Fri, 2005-02-18 at 22:41, Xin Zhao wrote:
> Thanks for your advice. I tried rmb() and wmb() before I sent last email,
> they does not help.
> 
> Actually I am running a single processor core. :( So it should not have
> any delay. But I still ran into the problem. Another interesting thing is
> that my working flow should be as follows:
> 
> domU issue a request -> generate an irq at dom0 -> domU waits for reply->
> dom0 gets the request, processes it and reply -> domU wakes up by irq
> caused by notification event sent by dom0, gets the result -> DomU sends
> another request
> 
> That means, if domU does not get the irq from dom0, it will not issue next
> request. Because of the problem of req_prod updates, dom0 failed to get
> the request and thus will not process it, not mention to reply. So dom0
> should not be able to receive next request or next irq.
> 
> But the fact is that dom0 can still get irq even it failed to get last
> request. It appears that dom0 issues multiple irqs for one event. How
> could that happed?
> 
> -x
> 
> 
> On Fri, 18 Feb 2005, Christopher Clark wrote:
> 
> > Are you running this on a single processor core?
> >
> > If not, it sounds to me like a cache coherency issue - you'll need a
> > write memory barrier after writing to the req_prod.  If you're using
> > the ring macros from io/ring.h this should be already taken care of
> > for you in the push macros.
> >
> > c.
> >
> >
> > On Fri, 18 Feb 2005 16:44:30 -0500 (EST), Xin Zhao
> > <zhaoxin@xxxxxxxxxxxxxx> wrote:
> > > I ran into the following problem:
> > >
> > > I setup a shared ring page and an event channel between two domains (dom0
> > > and one domU), DomU increases req_prod by one and notify the dom0 via the
> > > event channel, dom0 then check req_prod pointer and process the request in
> > > the shared ring. But I noticed that sometimes dom0 get the irq triggered
> > > by the notification event, but the req_prod remains the same. This
> > > situation only happened occasionally. Why? Because the req_prod is saved
> > > in the shared, mapped page, I suspect that there is a delay of updates
> > > between two domains. Is that true? If so, how to handle this problem?
> > >
> > > Your advice is highly appreciated!
> > >
> > > -x
> > >
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> >



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