I figure out what is going on here. The timing stats convert exit durations into microseconds. The problem is that any exits that take less than 1us will wind up having a duration of 0. After to changing to count timebase ticks instead, the numbers add up. By the way-- there aren't any instructions accounted for, even though they don't cover 100% of the handler-- any instructions that run before reading the timestamp will get accounted to the guest. Stuart > -----Original Message----- > From: Hollis Blanchard [mailto:hollis_blanchard@xxxxxxxxxx] > Sent: Thursday, December 02, 2010 12:38 PM > To: Yoder Stuart-B08248 > Cc: kvm-ppc@xxxxxxxxxxxxxxx > Subject: Re: kvm ppc timing stats > > I don't think the numbers added up like that for us either. We treated them > as relative data, not absolute. > > I don't remember how early/late the timestamps were recorded, but obviously > they cannot cover 100% of the handler. As the number of exits increases, > those unaccounted-for instructions would add up... but I wouldn't expect > that to cause errors of the magnitude you're seeing. > Perhaps there is a more obvious problem with the way certain exit types are > recorded (or not recorded). > > Hollis Blanchard > Mentor Graphics, Embedded Systems Division > > > On 12/01/2010 08:18 PM, Yoder Stuart-B08248 wrote: > > Well, in the example I'm looking at, which runs for 30 seconds, the > > "sum" column of the stats adds up to > > about 10 seconds total. So, there is 20 seconds > > unaccounted for. > > > > Interestingly enough, if I let the guest just sit idle for 30 seconds, > > the stats do sum up to about 30 seconds. > > > > Will get to the bottom of it, but wanted to make sure I was not > > missing something obvious. > > > > Stuart > > > > > >> -----Original Message----- > >> From: Hollis Blanchard [mailto:hollis_blanchard@xxxxxxxxxx] > >> Sent: Wednesday, December 01, 2010 6:27 PM > >> To: Yoder Stuart-B08248 > >> Cc: kvm-ppc@xxxxxxxxxxxxxxx > >> Subject: Re: kvm ppc timing stats > >> > >> Yes, your understanding is correct (barring any bugs, of course). Why > > do > >> you think "time is missing"? > >> > >> Hollis Blanchard > >> Mentor Graphics, Embedded Systems Division > >> > >> > >> On 12/01/2010 12:02 PM, Yoder Stuart-B08248 wrote: > >>> Hollis, > >>> > >>> Am looking at some performance data and want to make sure that > >>> > >>> I'm understanding things correctly with your CONFIG_KVM_EXIT_TIMING > >>> > >>> stuff. If I reset the timing counters, run a workload > >>> > >>> under for a fixed duration (e.g. 30 seconds), and then look > >>> > >>> at the exit stats, I should see 30 seconds worth of time accounted > >>> > >>> for, correct? > >>> > >>> Right now I'm seeing a substantial amount of time "missing" and > >>> > >>> want to make sure I'm not missing something. > >>> > >>> Stuart > >>> > > -- To unsubscribe from this list: send the line "unsubscribe kvm-ppc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
