Commit-ID: 8d4c00dc38a8aa30dae8402955e55e7b34e74bc8 Gitweb: https://git.kernel.org/tip/8d4c00dc38a8aa30dae8402955e55e7b34e74bc8 Author: Xunlei Pang <xlp...@linux.alibaba.com> AuthorDate: Mon, 9 Jul 2018 22:58:43 +0800 Committer: Ingo Molnar <mi...@kernel.org> CommitDate: Mon, 16 Jul 2018 00:28:31 +0200
sched/cputime: Ensure accurate utime and stime ratio in cputime_adjust() If users access "/proc/pid/stat", the utime and stime ratio in the current SAMPLE period are excepted, but currently cputime_adjust() always calculates with the ratio of the WHOLE lifetime of the process. This results in inaccurate utime and stime in "/proc/pid/stat". For example, a process runs for a while with "50% usr, 0% sys", then followed by "100% sys". For later while, the following is excepted: 0.0 usr, 100.0 sys but we get: 10.0 usr, 90.0 sys This patch uses the accurate ratio in cputime_adjust() to address the issue. A new 'task_cputime' type field is added in prev_cputime to record previous 'task_cputime' so that we can get the elapsed times as the accurate ratio. Signed-off-by: Xunlei Pang <xlp...@linux.alibaba.com> Cc: Frederic Weisbecker <frede...@kernel.org> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Luiz Capitulino <lcapitul...@redhat.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Tejun Heo <t...@kernel.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: baoyou....@gmail.com Link: http://lkml.kernel.org/r/20180709145843.126583-1-xlp...@linux.alibaba.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- include/linux/sched.h | 34 ++++++++++++------------ include/linux/sched/cputime.h | 12 ++++++++- kernel/sched/cputime.c | 61 ++++++++++++++++--------------------------- 3 files changed, 52 insertions(+), 55 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 43731fe51c97..fedc69d4a425 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -223,10 +223,27 @@ 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 * @stime: time spent in system mode + * @cputime: previous task_cputime to calculate utime/stime * @lock: protects the above two fields * * Stores previous user/system time values such that we can guarantee @@ -236,26 +253,11 @@ 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 @@ drop_precision: 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;
