[GIT PULL] scheduler fixes

Ingo Molnar
2016-08-19T00:54:00Z

Linus,

Please pull the latest sched-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

# HEAD: 03cbc732639ddcad15218c4b2046d255851ff1e3 sched/cputime: Resync steal time when guest & host lose sync

Two cputime fixes - hopefully the last ones.

Thanks,

Ingo

------------------>
Peter Zijlstra (1):
sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression

Wanpeng Li (1):
sched/cputime: Resync steal time when guest & host lose sync

kernel/sched/cputime.c | 33 +++++++++++++++++++++++++--------
1 file changed, 25 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 9858266fb0b3..a846cf89eb96 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -263,6 +263,11 @@ void account_idle_time(cputime_t cputime)
cpustat[CPUTIME_IDLE] += (__force u64) cputime;
}

+/*
+ * When a guest is interrupted for a longer amount of time, missed clock
+ * ticks are not redelivered later. Due to that, this function may on
+ * occasion account more time than the calling functions think elapsed.
+ */
static __always_inline cputime_t steal_account_process_time(cputime_t maxtime)
{
#ifdef CONFIG_PARAVIRT
@@ -371,7 +376,7 @@ static void irqtime_account_process_tick(struct task_struct *p, int user_tick,
* idle, or potentially user or system time. Due to rounding,
* other time can exceed ticks occasionally.
*/
- other = account_other_time(cputime);
+ other = account_other_time(ULONG_MAX);
if (other >= cputime)
return;
cputime -= other;
@@ -486,7 +491,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
}

cputime = cputime_one_jiffy;
- steal = steal_account_process_time(cputime);
+ steal = steal_account_process_time(ULONG_MAX);

if (steal >= cputime)
return;
@@ -516,7 +521,7 @@ void account_idle_ticks(unsigned long ticks)
}

cputime = jiffies_to_cputime(ticks);
- steal = steal_account_process_time(cputime);
+ steal = steal_account_process_time(ULONG_MAX);

if (steal >= cputime)
return;
@@ -614,19 +619,25 @@ static void cputime_adjust(struct task_cputime *curr,
stime = curr->stime;
utime = curr->utime;

- if (utime == 0) {
- stime = rtime;
+ /*
+ * If either stime or both stime and utime are 0, assume all runtime is
+ * userspace. Once a task gets some ticks, the monotonicy code at
+ * 'update' will ensure things converge to the observed ratio.
+ */
+ if (stime == 0) {
+ utime = rtime;
goto update;
}

- if (stime == 0) {
- utime = rtime;
+ if (utime == 0) {
+ stime = rtime;
goto update;
}

stime = scale_stime((__force u64)stime, (__force u64)rtime,
(__force u64)(stime + utime));

+update:
/*
* Make sure stime doesn't go backwards; this preserves monotonicity
* for utime because rtime is monotonic.
@@ -649,7 +660,6 @@ static void cputime_adjust(struct task_cputime *curr,
stime = rtime - utime;
}

-update:
prev->stime = stime;
prev->utime = utime;
out:
@@ -694,6 +704,13 @@ static cputime_t get_vtime_delta(struct task_struct *tsk)
unsigned long now = READ_ONCE(jiffies);
cputime_t delta, other;

+ /*
+ * Unlike tick based timing, vtime based timing never has lost
+ * ticks, and no need for steal time accounting to make up for
+ * lost ticks. Vtime accounts a rounded version of actual
+ * elapsed time. Limit account_other_time to prevent rounding
+ * errors from causing elapsed vtime to go negative.
+ */
delta = jiffies_to_cputime(now - tsk->vtime_snap);
other = account_other_time(delta);
WARN_ON_ONCE(tsk->vtime_snap_whence == VTIME_INACTIVE);