From: Wanpeng Li <[email protected]> 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. both guest and host are latest 4.7-rc1, 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 warps and then steal_jiffies overflow, this patch align prev_steal_time to the new steal clock timestamp, in order to avoid overflow and st stuff can continue to work. Cc: Ingo Molnar <[email protected]> Cc: Peter Zijlstra (Intel) <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Frederic Weisbecker <[email protected]> Cc: Paolo Bonzini <[email protected]> Cc: Radim <[email protected]> Signed-off-by: Wanpeng Li <[email protected]> --- kernel/sched/cputime.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 75f98c5..d0eebc3 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -265,7 +265,13 @@ static __always_inline bool steal_account_process_tick(void) unsigned long steal_jiffies; steal = paravirt_steal_clock(smp_processor_id()); - steal -= this_rq()->prev_steal_time; + if (likely(steal > this_rq()->prev_steal_time)) + steal -= this_rq()->prev_steal_time; + else { + /* steal clock warp */ + this_rq()->prev_steal_time = steal; + return false; + } /* * steal is in nsecs but our caller is expecting steal -- 1.9.1
