sched/cputime: Guarantee stime + utime == rtime
While the current code guarantees monotonicity for stime and utime
independently of one another, it does not guarantee that the sum of
both is equal to the total time we started out with.
This confuses things (and peoples) who look at this sum, like top, and
will report >100% usage followed by a matching period of 0%.
Rework the code to provide both individual monotonicity and a coherent
sum.
Suggested-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Reported-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Tested-by: Fredrik Markstrom <fredrik.markstrom@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: jason.low2@hp.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/kernel/fork.c b/kernel/fork.c
index 1bfefc6..6e8f807 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1067,6 +1067,7 @@
rcu_assign_pointer(tsk->sighand, sig);
if (!sig)
return -ENOMEM;
+
atomic_set(&sig->count, 1);
memcpy(sig->action, current->sighand->action, sizeof(sig->action));
return 0;
@@ -1128,6 +1129,7 @@
init_sigpending(&sig->shared_pending);
INIT_LIST_HEAD(&sig->posix_timers);
seqlock_init(&sig->stats_lock);
+ prev_cputime_init(&sig->prev_cputime);
hrtimer_init(&sig->real_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
sig->real_timer.function = it_real_fn;
@@ -1335,9 +1337,8 @@
p->utime = p->stime = p->gtime = 0;
p->utimescaled = p->stimescaled = 0;
-#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
- p->prev_cputime.utime = p->prev_cputime.stime = 0;
-#endif
+ prev_cputime_init(&p->prev_cputime);
+
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
seqlock_init(&p->vtime_seqlock);
p->vtime_snap = 0;