When a task runs on a housekeeper (a CPU running with the periodic tick with neighbours running tickless), it doesn't account cputime using vtime but relies on the tick. Such a task has its vtime_snap_whence value set to VTIME_INACTIVE.
Readers won't handle that correctly though. As long as vtime is running on some CPU, readers incorretly assume that vtime runs on all CPUs and always compute the tickless cputime delta, which is only junk on housekeepers. So lets fix this with checking that the target runs on a vtime CPU through the appropriate state check before computing the tickless delta. Cc: Christoph Lameter <[email protected]> Cc: Chris Metcalf <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Luiz Capitulino <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Hiroshi Shimamoto <[email protected]> Signed-off-by: Frederic Weisbecker <[email protected]> --- kernel/sched/cputime.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 4a18a6e..5cf24e7 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -795,7 +795,7 @@ cputime_t task_gtime(struct task_struct *t) seq = read_seqbegin(&t->vtime_seqlock); gtime = t->gtime; - if (t->flags & PF_VCPU) + if (t->vtime_snap_whence == VTIME_SYS && t->flags & PF_VCPU) gtime += vtime_delta(t); } while (read_seqretry(&t->vtime_seqlock, seq)); -- 2.5.3 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
