The steal guest time accounting code assumes that cputime_t is based on jiffies. So when CONFIG_NO_HZ_FULL=y, which implies that cputime_t is based on nsecs, steal_account_process_tick() passes the delta in jiffies to account_steal_time() which then accounts it as if it's a value in nsecs.
As a result, accounting 1 second of steal time (with HZ=100 that would be 100 jiffies) is spuriously accounted as 100 nsecs. As such /proc/stat may report 0 values of steal time even when two guests have run concurrently for a few seconds on the same host and same CPU. In order to fix this, lets convert the nsecs based steal delta to cputime instead of jiffies by using the right conversion API. Given that the steal time is stored in cputime_t and this type can have a smaller granularity than nsecs, we only account the rounded converted value and leave the remaining nsecs for the next deltas. Reported-by: Huiqingding <[email protected]> Reported-by: Marcelo Tosatti <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Marcelo Tosatti <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> --- kernel/sched/cputime.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 9994791..e3d2612 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -258,16 +258,17 @@ static __always_inline bool steal_account_process_tick(void) { #ifdef CONFIG_PARAVIRT if (static_key_false(¶virt_steal_enabled)) { - u64 steal, st = 0; + u64 steal; + cputime_t steal_ct; steal = paravirt_steal_clock(smp_processor_id()); steal -= this_rq()->prev_steal_time; - st = steal_ticks(steal); - this_rq()->prev_steal_time += st * TICK_NSEC; + steal_ct = nsecs_to_cputime(steal); + this_rq()->prev_steal_time += cputime_to_nsecs(steal_ct); - account_steal_time(st); - return st; + account_steal_time(steal_ct); + return steal_ct; } #endif return false; -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
