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Subject[tip: sched/core] sched/vtime: Bring up complete kcpustat accessor
The following commit has been merged into the sched/core branch of tip:

Commit-ID: 74722bb223d0f236303b60c9509ff924a9713780
Gitweb: https://git.kernel.org/tip/74722bb223d0f236303b60c9509ff924a9713780
Author: Frederic Weisbecker <frederic@kernel.org>
AuthorDate: Thu, 21 Nov 2019 03:44:26 +01:00
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 21 Nov 2019 07:33:24 +01:00

sched/vtime: Bring up complete kcpustat accessor

Many callsites want to fetch the values of system, user, user_nice, guest
or guest_nice kcpustat fields altogether or at least a pair of these.

In that case calling kcpustat_field() for each requested field brings
unecessary overhead when we could fetch all of them in a row.

So provide kcpustat_cpu_fetch() that fetches the whole kcpustat array
in a vtime safe way under the same RCU and seqcount block.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191121024430.19938-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
include/linux/kernel_stat.h | 7 ++-
kernel/sched/cputime.c | 136 +++++++++++++++++++++++++++++------
2 files changed, 123 insertions(+), 20 deletions(-)

diff --git a/include/linux/kernel_stat.h b/include/linux/kernel_stat.h
index 7978119..89f0745 100644
--- a/include/linux/kernel_stat.h
+++ b/include/linux/kernel_stat.h
@@ -81,12 +81,19 @@ static inline unsigned int kstat_cpu_irqs_sum(unsigned int cpu)
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
extern u64 kcpustat_field(struct kernel_cpustat *kcpustat,
enum cpu_usage_stat usage, int cpu);
+extern void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu);
#else
static inline u64 kcpustat_field(struct kernel_cpustat *kcpustat,
enum cpu_usage_stat usage, int cpu)
{
return kcpustat->cpustat[usage];
}
+
+static inline void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu)
+{
+ *dst = kcpustat_cpu(cpu);
+}
+
#endif

extern void account_user_time(struct task_struct *, u64);
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index 27b5406..d43318a 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -912,6 +912,30 @@ void task_cputime(struct task_struct *t, u64 *utime, u64 *stime)
} while (read_seqcount_retry(&vtime->seqcount, seq));
}

+static int vtime_state_check(struct vtime *vtime, int cpu)
+{
+ /*
+ * We raced against a context switch, fetch the
+ * kcpustat task again.
+ */
+ if (vtime->cpu != cpu && vtime->cpu != -1)
+ return -EAGAIN;
+
+ /*
+ * Two possible things here:
+ * 1) We are seeing the scheduling out task (prev) or any past one.
+ * 2) We are seeing the scheduling in task (next) but it hasn't
+ * passed though vtime_task_switch() yet so the pending
+ * cputime of the prev task may not be flushed yet.
+ *
+ * Case 1) is ok but 2) is not. So wait for a safe VTIME state.
+ */
+ if (vtime->state == VTIME_INACTIVE)
+ return -EAGAIN;
+
+ return 0;
+}
+
static u64 kcpustat_user_vtime(struct vtime *vtime)
{
if (vtime->state == VTIME_USER)
@@ -933,26 +957,9 @@ static int kcpustat_field_vtime(u64 *cpustat,
do {
seq = read_seqcount_begin(&vtime->seqcount);

- /*
- * We raced against context switch, fetch the
- * kcpustat task again.
- */
- if (vtime->cpu != cpu && vtime->cpu != -1)
- return -EAGAIN;
-
- /*
- * Two possible things here:
- * 1) We are seeing the scheduling out task (prev) or any past one.
- * 2) We are seeing the scheduling in task (next) but it hasn't
- * passed though vtime_task_switch() yet so the pending
- * cputime of the prev task may not be flushed yet.
- *
- * Case 1) is ok but 2) is not. So wait for a safe VTIME state.
- */
- if (vtime->state == VTIME_INACTIVE)
- return -EAGAIN;
-
- err = 0;
+ err = vtime_state_check(vtime, cpu);
+ if (err < 0)
+ return err;

*val = cpustat[usage];

@@ -1025,4 +1032,93 @@ u64 kcpustat_field(struct kernel_cpustat *kcpustat,
}
}
EXPORT_SYMBOL_GPL(kcpustat_field);
+
+static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst,
+ const struct kernel_cpustat *src,
+ struct task_struct *tsk, int cpu)
+{
+ struct vtime *vtime = &tsk->vtime;
+ unsigned int seq;
+ int err;
+
+ do {
+ u64 *cpustat;
+ u64 delta;
+
+ seq = read_seqcount_begin(&vtime->seqcount);
+
+ err = vtime_state_check(vtime, cpu);
+ if (err < 0)
+ return err;
+
+ *dst = *src;
+ cpustat = dst->cpustat;
+
+ /* Task is sleeping, dead or idle, nothing to add */
+ if (vtime->state < VTIME_SYS)
+ continue;
+
+ delta = vtime_delta(vtime);
+
+ /*
+ * Task runs either in user (including guest) or kernel space,
+ * add pending nohz time to the right place.
+ */
+ if (vtime->state == VTIME_SYS) {
+ cpustat[CPUTIME_SYSTEM] += vtime->stime + delta;
+ } else if (vtime->state == VTIME_USER) {
+ if (task_nice(tsk) > 0)
+ cpustat[CPUTIME_NICE] += vtime->utime + delta;
+ else
+ cpustat[CPUTIME_USER] += vtime->utime + delta;
+ } else {
+ WARN_ON_ONCE(vtime->state != VTIME_GUEST);
+ if (task_nice(tsk) > 0) {
+ cpustat[CPUTIME_GUEST_NICE] += vtime->gtime + delta;
+ cpustat[CPUTIME_NICE] += vtime->gtime + delta;
+ } else {
+ cpustat[CPUTIME_GUEST] += vtime->gtime + delta;
+ cpustat[CPUTIME_USER] += vtime->gtime + delta;
+ }
+ }
+ } while (read_seqcount_retry(&vtime->seqcount, seq));
+
+ return err;
+}
+
+void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu)
+{
+ const struct kernel_cpustat *src = &kcpustat_cpu(cpu);
+ struct rq *rq;
+ int err;
+
+ if (!vtime_accounting_enabled_cpu(cpu)) {
+ *dst = *src;
+ return;
+ }
+
+ rq = cpu_rq(cpu);
+
+ for (;;) {
+ struct task_struct *curr;
+
+ rcu_read_lock();
+ curr = rcu_dereference(rq->curr);
+ if (WARN_ON_ONCE(!curr)) {
+ rcu_read_unlock();
+ *dst = *src;
+ return;
+ }
+
+ err = kcpustat_cpu_fetch_vtime(dst, src, curr, cpu);
+ rcu_read_unlock();
+
+ if (!err)
+ return;
+
+ cpu_relax();
+ }
+}
+EXPORT_SYMBOL_GPL(kcpustat_cpu_fetch);
+
#endif /* CONFIG_VIRT_CPU_ACCOUNTING_GEN */
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