[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Re: change hvm defaults for timer_mode and hpet?
I'm happy for the defaults to change. Send a patch. -- Keir On 3/6/08 20:47, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote: > Due to recent changes in timer handling (specifically building > hpet emulation on top of Xen system time and ensuring it is > monotonic), I wonder if it now makes sense to: > > 1) change hvm default for hpet to 1 (was 0) > 2) change hvm timer_mode default from 0 to 2 > > I encouraged adding the hvm hpet parameter and defaulting > it to 0 because the virtual hpet was not reliable and many > guests/versions default to using hpet (by default) it if > it is available. That reliability problem should now be fixed. > > Timer_mode==0 is necessary for guests that do not have > a monotonic platform timer; each processor in a multi-VCPU > guest has to do its best using only pit-generated ticks and > lost ticks mean lost time, so Xen does its best to squirrel > away any ticks that occur while a VCPU is asleep and deliver > all of them when the VCPU awakens. Thus time moves forward > independently on each VCPU, leading to potential unavoidable > "Time went backwards" problems. With virtual hpet > working properly, timer_mode==0 should rarely be necessary, > though I think we should leave it around for pre-hpet-capable > guests. > > Although both of these parameters are easily specified in the > hvm config file, both are obscure and difficult to explain. > It would be nice if they were "right" most of the time and > only needed to be specified/explained for corner cases. > > Comments? It would be nice to get this all settled (and fully > tested) prior to 3.3. > > Thanks, > Dan > > > =================================== > Thanks... for the memory > I really could use more / My throughput's on the floor > The balloon is flat / My swap disk's fat / I've OOM's in store > Overcommitted so much > (with apologies to the late great Bob Hope) _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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