On Fri, 2016-06-03 at 13:21 +0800, Wanpeng Li wrote: > From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > > I observed that sometimes st is 100% instantaneous, then idle is > 100% > even if there is a cpu hog on the guest cpu after the cpu hotplug > comes > back(N.B. this can not always be readily reproduced). I add trace to > capture it as below: > > cpuhp/1-12 [001] d.h1 167.461657: account_process_tick: steal = > 1291385514, prev_steal_time = 0 > cpuhp/1-12 [001] d.h1 167.461659: account_process_tick: > steal_jiffies = 1291 > <idle>-0 [001] d.h1 167.462663: account_process_tick: steal = > 18732255, prev_steal_time = 1291000000 > <idle>-0 [001] d.h1 167.462664: account_process_tick: > steal_jiffies = 18446744072437 > > The steal clock warp and then steal_jiffies overflow. > > Rik also pointed out to me: > > > > > I have seen stuff like that with live migration too, in the past > This patch adds steal clock warp handling by a safe threshold to > only > apply steal times that are positive and smaller than one second (as > long as nohz_full has the one second timer tick left), ignoring > intervals > that are negative or longer than a second, and using those to sync > up > the guest with the host. > > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> > Cc: Rik van Riel <riel@xxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: Radim <rkrcmar@xxxxxxxxxx> > Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx> > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> -- All Rights Reversed.
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