From 173be9a14f7b2e901cf77c18b1aafd4d672e9d9e Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 15 Aug 2016 18:38:42 +0200 Subject: [PATCH] sched/cputime: Fix NO_HZ_FULL getrusage() monotonicity regression Mike reports: Roughly 10% of the time, ltp testcase getrusage04 fails: getrusage04 0 TINFO : Expected timers granularity is 4000 us getrusage04 0 TINFO : Using 1 as multiply factor for max [us]time increment (1000+4000us)! getrusage04 0 TINFO : utime: 0us; stime: 179us getrusage04 0 TINFO : utime: 3751us; stime: 0us getrusage04 1 TFAIL : getrusage04.c:133: stime increased > 5000us: And tracked it down to the case where the task simply doesn't get _any_ [us]time ticks. Update the code to assume all rtime is utime when we lack information, thus ensuring a task that elides the tick gets time accounted. Reported-by: Mike Galbraith Tested-by: Mike Galbraith Signed-off-by: Peter Zijlstra (Intel) Cc: Frederic Weisbecker Cc: Fredrik Markstrom Cc: Linus Torvalds Cc: Paolo Bonzini Cc: Peter Zijlstra Cc: Radim Cc: Rik van Riel Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Cc: Wanpeng Li Cc: stable@vger.kernel.org # 4.3+ Fixes: 9d7fb0427648 ("sched/cputime: Guarantee stime + utime == rtime") Signed-off-by: Ingo Molnar --- kernel/sched/cputime.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 9858266fb0b3..2ee83b200504 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -614,19 +614,25 @@ 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 +655,6 @@ static void cputime_adjust(struct task_cputime *curr, stime = rtime - utime; } -update: prev->stime = stime; prev->utime = utime; out: -- 2.20.1