Re: [Xen-devel] asterisk, ztdummy, and usb (and HZ = 100 under xen ???)

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 21 May 2005, at 08:53, James Harper wrote:

> It's not as straight forward as that. Asterisk needs a 1000hz timer for
> certain functions to work. For certain things to work really properly
> (eg fax), this timer needs to be synchronised exactly to the exchange
> (eg from the isdn/e1 card) otherwise frames might be dropped.
>
> Under 2.4, the ztdummy driver uses the UHCI USB hardware to get a 
> 1000hz
> interval. Under 2.6, HZ=1000 (on the x86 anyway, except under xen :) so
> it counts jiffies instead. If you have HZ=100 then you can't get 1000
> ticks from it no matter what macro you use, so the best you could do
> would be to fall back to UHCI timing when HZ is not evenly divisible by
> 1000, or fail if no UHCI controller is present.
>
> I'm surprised my patch (eg generate 10 ticks ever 1/100 seconds) works
> as well as it does.
We're going to rip the fixed ticker out of Xen and allow domains to 
specify a background ticker at a rate of their choice, which ought to 
fix this for you. OF course, you're pretty screwed running this kind of 
thing on Xen unless you dedicate a whole CPU to the relevant domain.
 -- Keir


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel