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Message-Id: <20180622071542.61569-1-xlpang@linux.alibaba.com>
Date: Fri, 22 Jun 2018 15:15:42 +0800
From: Xunlei Pang <xlpang@...ux.alibaba.com>
To: Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Frederic Weisbecker <frederic@...nel.org>,
Tejun Heo <tj@...nel.org>
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] sched/cputime: Ensure correct utime and stime proportion
We use per-cgroup cpu usage statistics similar to "cgroup rstat",
and encountered a problem that user and sys usages are wrongly
split sometimes.
Run tasks with some random run-sleep pattern for a long time, and
when tick-based time and scheduler sum_exec_runtime hugely drifts
apart(scheduler sum_exec_runtime is less than tick-based time),
the current implementation of cputime_adjust() will produce less
sys usage than the actual use after changing to run a different
workload pattern with high sys. This is because total tick-based
utime and stime are used to split the total sum_exec_runtime.
Same problem exists on utime and stime from "/proc/<pid>/stat".
[Example]
Run some random run-sleep patterns for minutes, then change to run
high sys pattern, and watch.
1) standard "top"(which is the correct one):
4.6 us, 94.5 sy, 0.0 ni, 0.9 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
2) our tool parsing utime and stime from "/proc/<pid>/stat":
20.5 usr, 78.4 sys
We can see "20.5 usr" displayed in 2) was incorrect, it recovers
gradually with time: 9.7 usr, 89.5 sys
This patch fixes the issue by calculating using all kinds of time
elapsed since last parse in cputime_adjust(), and accumulate the
corresponding results calculated into prev_cputime. A new field
of task_cputime type is added in structure prev_cputime to record
previous task_cputime so that we can get the elapsed time deltas.
Signed-off-by: Xunlei Pang <xlpang@...ux.alibaba.com>
---
include/linux/sched.h | 33 +++++++++++------------
include/linux/sched/cputime.h | 12 ++++++++-
kernel/sched/cputime.c | 61 ++++++++++++++++---------------------------
3 files changed, 51 insertions(+), 55 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 87bf02d93a27..5108ac8414e0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -223,6 +223,22 @@ extern void io_schedule_finish(int token);
extern long io_schedule_timeout(long timeout);
extern void io_schedule(void);
+/**
+ * struct task_cputime - collected CPU time counts
+ * @utime: time spent in user mode, in nanoseconds
+ * @stime: time spent in kernel mode, in nanoseconds
+ * @sum_exec_runtime: total time spent on the CPU, in nanoseconds
+ *
+ * This structure groups together three kinds of CPU time that are tracked for
+ * threads and thread groups. Most things considering CPU time want to group
+ * these counts together and treat all three of them in parallel.
+ */
+struct task_cputime {
+ u64 utime;
+ u64 stime;
+ unsigned long long sum_exec_runtime;
+};
+
/**
* struct prev_cputime - snapshot of system and user cputime
* @utime: time spent in user mode
@@ -236,26 +252,11 @@ struct prev_cputime {
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
u64 utime;
u64 stime;
+ struct task_cputime cputime;
raw_spinlock_t lock;
#endif
};
-/**
- * struct task_cputime - collected CPU time counts
- * @utime: time spent in user mode, in nanoseconds
- * @stime: time spent in kernel mode, in nanoseconds
- * @sum_exec_runtime: total time spent on the CPU, in nanoseconds
- *
- * This structure groups together three kinds of CPU time that are tracked for
- * threads and thread groups. Most things considering CPU time want to group
- * these counts together and treat all three of them in parallel.
- */
-struct task_cputime {
- u64 utime;
- u64 stime;
- unsigned long long sum_exec_runtime;
-};
-
/* Alternate field names when used on cache expirations: */
#define virt_exp utime
#define prof_exp stime
diff --git a/include/linux/sched/cputime.h b/include/linux/sched/cputime.h
index 53f883f5a2fd..49f8fd2564ed 100644
--- a/include/linux/sched/cputime.h
+++ b/include/linux/sched/cputime.h
@@ -175,10 +175,20 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
atomic64_add(ns, &cputimer->cputime_atomic.sum_exec_runtime);
}
-static inline void prev_cputime_init(struct prev_cputime *prev)
+static inline void prev_cputime_clear(struct prev_cputime *prev)
{
#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
prev->utime = prev->stime = 0;
+ prev->cputime.utime = 0;
+ prev->cputime.stime = 0;
+ prev->cputime.sum_exec_runtime = 0;
+#endif
+}
+
+static inline void prev_cputime_init(struct prev_cputime *prev)
+{
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
+ prev_cputime_clear(prev);
raw_spin_lock_init(&prev->lock);
#endif
}
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 0796f938c4f0..a68483ee3ad7 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -590,69 +590,54 @@ static u64 scale_stime(u64 stime, u64 rtime, u64 total)
void cputime_adjust(struct task_cputime *curr, struct prev_cputime *prev,
u64 *ut, u64 *st)
{
- u64 rtime, stime, utime;
+ u64 rtime_delta, stime_delta, utime_delta;
unsigned long flags;
/* Serialize concurrent callers such that we can honour our guarantees */
raw_spin_lock_irqsave(&prev->lock, flags);
- rtime = curr->sum_exec_runtime;
/*
* This is possible under two circumstances:
- * - rtime isn't monotonic after all (a bug);
+ * - task_cputime isn't monotonic after all (a bug);
* - we got reordered by the lock.
*
* In both cases this acts as a filter such that the rest of the code
* can assume it is monotonic regardless of anything else.
*/
- if (prev->stime + prev->utime >= rtime)
+ if (prev->cputime.utime > curr->utime ||
+ prev->cputime.stime > curr->stime ||
+ prev->cputime.sum_exec_runtime >= curr->sum_exec_runtime)
goto out;
- stime = curr->stime;
- utime = curr->utime;
+ stime_delta = curr->stime - prev->cputime.stime;
+ utime_delta = curr->utime - prev->cputime.utime;
+ rtime_delta = curr->sum_exec_runtime - prev->cputime.sum_exec_runtime;
/*
- * If either stime or 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 either stime or utime increase 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;
+ if (stime_delta == 0) {
+ utime_delta = rtime_delta;
goto update;
}
- if (utime == 0) {
- stime = rtime;
+ if (utime_delta == 0) {
+ stime_delta = rtime_delta;
goto update;
}
- stime = scale_stime(stime, rtime, stime + utime);
+ stime_delta = scale_stime(stime_delta, rtime_delta,
+ stime_delta + utime_delta);
+ if (stime_delta > rtime_delta)
+ stime_delta = rtime_delta;
+ utime_delta = rtime_delta - stime_delta;
update:
- /*
- * Make sure stime doesn't go backwards; this preserves monotonicity
- * for utime because rtime is monotonic.
- *
- * utime_i+1 = rtime_i+1 - stime_i
- * = rtime_i+1 - (rtime_i - utime_i)
- * = (rtime_i+1 - rtime_i) + utime_i
- * >= utime_i
- */
- if (stime < prev->stime)
- stime = prev->stime;
- utime = rtime - stime;
-
- /*
- * Make sure utime doesn't go backwards; this still preserves
- * monotonicity for stime, analogous argument to above.
- */
- if (utime < prev->utime) {
- utime = prev->utime;
- stime = rtime - utime;
- }
-
- prev->stime = stime;
- prev->utime = utime;
+ prev->cputime = *curr;
+ prev->utime += utime_delta;
+ prev->stime += stime_delta;
out:
*ut = prev->utime;
*st = prev->stime;
--
2.14.1.40.g8e62ba1
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