Messages in this thread | | | From | Ferenc Wagner <> | Subject | Re: [PATCH] cpu idle ticks show twice in xen pvm guest | Date | Fri, 09 Dec 2011 16:47:39 +0100 |
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Jeremy Fitzhardinge <jeremy@goop.org> writes:
>> On Wed, Oct 05, 2011 at 10:11:58PM -0700, Zhenzhong Duan wrote: >> >>> Run below test on xen pvm. >>> # x=$(cat /proc/stat | grep cpu0 | awk '{print $5}') && sleep 60 \ >>> && y=$(cat /proc/stat | grep cpu0 | awk '{print $5}') \ >>> && echo -e "X:$x\nY:$y\nIDLE:" $(echo "scale=3; ($y-$x)/6000*100" | bc) >>> >>> @ X:58562301 >>> @ Y:58574282 >>> @ IDLE: 199.600 >>> >>> Normal idle percent should be around 100%. >>> xen_timer_interrupt called account_idle_ticks to account hypervisor stolen idle ticks >>> but these ticks will be accounted again when idle ticks restarted. >>> >>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com> >>> Signed-off-by: Joe Jin <joe.jin@oracle.com> > > Does this affect the accounting of stolen ticks? If it does, that's not > necessarily a showstopper for this patch, but we'll need to do some more > thinking about it. Certainly, accurate accounting for idleness is > important.
Please see also http://thread.gmane.org/gmane.linux.kernel/734441, where I found that the counter doubling isn't always present under 2.6.26. However, after going to 2.6.32 (Debian lenny-backports kernel, 4th of April on the graph below) that instability seems to disappear. Please note that the following graph shows halved idle and iowait percentages.
[image] (I haven't collected steal values, so the numbers don't sum up to 100%.) I'd be grateful if this discrepancy could be cleared up eventually! It's heartening to see some progress after more than three years. :)
Actually, as Munin doesn't half the idle and iowait values, but truncates the (then overflowing) graph at 100%, I was rather surprised to see iowait completely disappear after the kernel upgrade, and concluded that it was somehow converted into buggy-looping in blkfront. Now I see this isn't the case, but the steadily increasing system CPU usage between reboots is still a mystery. I'll start a separate thread for that, just wanted to provide some motivation for this topic. -- Thanks, Feri.
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