The problem that the statistical time goes backward, the value read first is 319, and the value read again is 318. As follows： first： cat /proc/stat | grep cpu1 cpu1 319 0 496 41665 0 0 0 0 0 0 then： cat /proc/stat | grep cpu1 cpu1 318 0 497 41674 0 0 0 0 0 0

Time goes back, which is counterintuitive.

After debug this, The problem is caused by the implementation of kcpustat_cpu_fetch_vtime. As follows：

CPU0 CPU1 First: show_stat(): ->kcpustat_cpu_fetch() ->kcpustat_cpu_fetch_vtime() ->cpustat[CPUTIME_USER] = kcpustat_cpu(cpu) + vtime->utime + delta; rq->curr is in user mod ---> When CPU1 rq->curr running on userspace, need add utime and delta ---> rq->curr->vtime->utime is less than 1 tick Then: show_stat(): ->kcpustat_cpu_fetch() ->kcpustat_cpu_fetch_vtime() ->cpustat[CPUTIME_USER] = kcpustat_cpu(cpu); rq->curr is in kernel mod ---> When CPU1 rq->curr running on kernel space, just got kcpustat

Fixes: 74722bb223d0 ("sched/vtime: Bring up complete kcpustat accessor") Signed-off-by: Li Hua hucool.lihua@huawei.com --- kernel/sched/core.c | 1 + kernel/sched/cputime.c | 33 ++++++++++++++++++++++++++++++++- kernel/sched/sched.h | 6 ++++++ 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 189999007f32..c542b61cab54 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -9753,6 +9753,7 @@ void __init sched_init(void)

rq->core_cookie = 0UL; #endif + cputime_cpu_init(i); }

set_load_weight(&init_task, false); diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 95fc77853743..ba3bcb40795e 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -1060,6 +1060,19 @@ static int kcpustat_cpu_fetch_vtime(struct kernel_cpustat *dst, return 0; }

+/* + * Stores the time of the last acquisition, which is used to handle the case of + * time backwards. + */ +static DEFINE_PER_CPU(struct kernel_cpustat, cpustat_prev); +static DEFINE_PER_CPU(raw_spinlock_t, cpustat_prev_lock); + +void cputime_cpu_init(int cpu) +{ + raw_spin_lock_init(per_cpu_ptr(&cpustat_prev_lock, cpu)); +} + + void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu) { const struct kernel_cpustat *src = &kcpustat_cpu(cpu); @@ -1087,8 +1100,26 @@ void kcpustat_cpu_fetch(struct kernel_cpustat *dst, int cpu) err = kcpustat_cpu_fetch_vtime(dst, src, curr, cpu); rcu_read_unlock();

- if (!err) + if (!err) { + int i; + int map[5] = {CPUTIME_USER, CPUTIME_SYSTEM, CPUTIME_NICE, + CPUTIME_GUEST, CPUTIME_GUEST_NICE}; + struct kernel_cpustat *prev = &per_cpu(cpustat_prev, cpu); + raw_spinlock_t *cpustat_lock = &per_cpu(cpustat_prev_lock, cpu); + u64 *dst_stat = dst->cpustat; + u64 *prev_stat = prev->cpustat; + + raw_spin_lock(cpustat_lock); + for (i = 0; i < 5; i++) { + int idx = map[i]; + + if (dst_stat[idx] < prev_stat[idx]) + dst_stat[idx] = prev_stat[idx]; + } + *prev = *dst; + raw_spin_unlock(cpustat_lock); return; + }

cpu_relax(); } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index a6f071b2acac..cbe09795a394 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3156,4 +3156,10 @@ extern int sched_dynamic_mode(const char *str); extern void sched_dynamic_update(int mode); #endif

+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN +extern void cputime_cpu_init(int cpu); +#else +static inline void cputime_cpu_init(int cpu) {} +#endif + #endif /* _KERNEL_SCHED_SCHED_H */