[PATCH -tip 4/4] cputime: remove scaling
From: Stanislaw Gruszka
Date: Thu Apr 04 2013 - 05:10:37 EST
Scaling cputime cause problems, bunch of them was fixed, but still is possible
to hit multiplication overflow issue, which make {u,s}time values incorrect.
This problem has no good solution in kernel.
This patch remove scaling code and export raw values of {u,t}ime . Procps
programs can use newly introduced sum_exec_runtime to find out precisely
calculated process cpu time and scale utime/stime values accordingly.
Unfortunately times(2) syscall has no such option.
This change affect kernels compiled without CONFIG_VIRT_CPU_ACCOUNTING_*.
Signed-off-by: Stanislaw Gruszka <sgruszka@xxxxxxxxxx>
---
fs/proc/array.c | 4 +-
include/linux/sched.h | 20 --------
kernel/exit.c | 4 +-
kernel/fork.c | 3 -
kernel/sched/cputime.c | 117 +-----------------------------------------------
kernel/sys.c | 6 +-
6 files changed, 8 insertions(+), 146 deletions(-)
diff --git a/fs/proc/array.c b/fs/proc/array.c
index 1444dc5..5feadc4 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -459,7 +459,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
min_flt += sig->min_flt;
maj_flt += sig->maj_flt;
- thread_group_cputime_adjusted(task, &cputime);
+ thread_group_cputime(task, &cputime);
utime = cputime.utime;
stime = cputime.stime;
sum_exec_runtime = cputime.sum_exec_runtime;
@@ -478,7 +478,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
if (!whole) {
min_flt = task->min_flt;
maj_flt = task->maj_flt;
- task_cputime_adjusted(task, &utime, &stime);
+ task_cputime(task, &utime, &stime);
sum_exec_runtime = task->se.sum_exec_runtime;
gtime = task_gtime(task);
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index c25772d..23c8ac3 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -397,18 +397,6 @@ struct cpu_itimer {
};
/**
- * struct cputime - snaphsot of system and user cputime
- * @utime: time spent in user mode
- * @stime: time spent in system mode
- *
- * Gathers a generic snapshot of user and system time.
- */
-struct cputime {
- cputime_t utime;
- cputime_t stime;
-};
-
-/**
* struct task_cputime - collected CPU time counts
* @utime: time spent in user mode, in &cputime_t units
* @stime: time spent in kernel mode, in &cputime_t units
@@ -558,9 +546,6 @@ struct signal_struct {
cputime_t utime, stime, cutime, cstime;
cputime_t gtime;
cputime_t cgtime;
-#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
- struct cputime prev_cputime;
-#endif
unsigned long nvcsw, nivcsw, cnvcsw, cnivcsw;
unsigned long min_flt, maj_flt, cmin_flt, cmaj_flt;
unsigned long inblock, oublock, cinblock, coublock;
@@ -1161,9 +1146,6 @@ struct task_struct {
cputime_t utime, stime, utimescaled, stimescaled;
cputime_t gtime;
-#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
- struct cputime prev_cputime;
-#endif
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
seqlock_t vtime_seqlock;
unsigned long long vtime_snap;
@@ -1597,8 +1579,6 @@ static inline cputime_t task_gtime(struct task_struct *t)
return t->gtime;
}
#endif
-extern void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st);
-extern void thread_group_cputime_adjusted(struct task_struct *p, struct task_cputime *ct);
/*
* Per process flags
diff --git a/kernel/exit.c b/kernel/exit.c
index fb158f1..b6bd7ae 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1084,11 +1084,11 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
* as other threads in the parent group can be right
* here reaping other children at the same time.
*
- * We use thread_group_cputime_adjusted() to get times for the thread
+ * We use thread_group_cputime() to get times for the thread
* group, which consolidates times for all threads in the
* group including the group leader.
*/
- thread_group_cputime_adjusted(p, &tg_cputime);
+ thread_group_cputime(p, &tg_cputime);
spin_lock_irq(&p->real_parent->sighand->siglock);
psig = p->real_parent->signal;
sig = p->signal;
diff --git a/kernel/fork.c b/kernel/fork.c
index 339f60d..2ae1706 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1233,9 +1233,6 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->utime = p->stime = p->gtime = 0;
p->utimescaled = p->stimescaled = 0;
-#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
- p->prev_cputime.utime = p->prev_cputime.stime = 0;
-#endif
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
seqlock_init(&p->vtime_seqlock);
p->vtime_snap = 0;
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index a600f7f..23df74b 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -448,19 +448,7 @@ EXPORT_SYMBOL_GPL(vtime_account_irq_enter);
#endif /* __ARCH_HAS_VTIME_ACCOUNT */
#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
-
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
-void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
-{
- *ut = p->utime;
- *st = p->stime;
-}
-
-void thread_group_cputime_adjusted(struct task_struct *p, struct task_cputime *cputime)
-{
- thread_group_cputime(p, cputime);
-}
-#else /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
+#ifndef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
/*
* Account a single tick of cpu time.
* @p: the process that the cpu time gets accounted to
@@ -516,109 +504,6 @@ void account_idle_ticks(unsigned long ticks)
account_idle_time(jiffies_to_cputime(ticks));
}
-/*
- * Perform (stime * rtime) / total with reduced chances
- * of multiplication overflows by using smaller factors
- * like quotient and remainders of divisions between
- * rtime and total.
- */
-static cputime_t scale_stime(u64 stime, u64 rtime, u64 total)
-{
- u64 rem, res, scaled;
-
- if (rtime >= total) {
- /*
- * Scale up to rtime / total then add
- * the remainder scaled to stime / total.
- */
- res = div64_u64_rem(rtime, total, &rem);
- scaled = stime * res;
- scaled += div64_u64(stime * rem, total);
- } else {
- /*
- * Same in reverse: scale down to total / rtime
- * then substract that result scaled to
- * to the remaining part.
- */
- res = div64_u64_rem(total, rtime, &rem);
- scaled = div64_u64(stime, res);
- scaled -= div64_u64(scaled * rem, total);
- }
-
- return (__force cputime_t) scaled;
-}
-
-/*
- * Adjust tick based cputime random precision against scheduler
- * runtime accounting.
- */
-static void cputime_adjust(struct task_cputime *curr,
- struct cputime *prev,
- cputime_t *ut, cputime_t *st)
-{
- cputime_t rtime, stime, total;
-
- if (vtime_accounting_enabled()) {
- *ut = curr->utime;
- *st = curr->stime;
- return;
- }
-
- stime = curr->stime;
- total = stime + curr->utime;
-
- /*
- * Tick based cputime accounting depend on random scheduling
- * timeslices of a task to be interrupted or not by the timer.
- * Depending on these circumstances, the number of these interrupts
- * may be over or under-optimistic, matching the real user and system
- * cputime with a variable precision.
- *
- * Fix this by scaling these tick based values against the total
- * runtime accounted by the CFS scheduler.
- */
- rtime = nsecs_to_cputime(curr->sum_exec_runtime);
-
- if (!rtime) {
- stime = 0;
- } else if (!total) {
- stime = rtime;
- } else {
- stime = scale_stime((__force u64)stime,
- (__force u64)rtime, (__force u64)total);
- }
-
- /*
- * If the tick based count grows faster than the scheduler one,
- * the result of the scaling may go backward.
- * Let's enforce monotonicity.
- */
- prev->stime = max(prev->stime, stime);
- prev->utime = max(prev->utime, rtime - prev->stime);
-
- *ut = prev->utime;
- *st = prev->stime;
-}
-
-void task_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime_t *st)
-{
- struct task_cputime cputime = {
- .sum_exec_runtime = p->se.sum_exec_runtime,
- };
-
- task_cputime(p, &cputime.utime, &cputime.stime);
- cputime_adjust(&cputime, &p->prev_cputime, ut, st);
-}
-
-/*
- * Must be called with siglock held.
- */
-void thread_group_cputime_adjusted(struct task_struct *p, struct task_cputime *cputime)
-{
- thread_group_cputime(p, cputime);
- cputime_adjust(cputime, &p->signal->prev_cputime,
- &cputime->utime, &cputime->stime);
-}
#endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
diff --git a/kernel/sys.c b/kernel/sys.c
index 2f555c1..00f143e 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1049,7 +1049,7 @@ void do_sys_times(struct tms *tms)
struct task_cputime tg_cputime;
spin_lock_irq(¤t->sighand->siglock);
- thread_group_cputime_adjusted(current, &tg_cputime);
+ thread_group_cputime(current, &tg_cputime);
cutime = current->signal->cutime;
cstime = current->signal->cstime;
spin_unlock_irq(¤t->sighand->siglock);
@@ -1708,7 +1708,7 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
utime = stime = 0;
if (who == RUSAGE_THREAD) {
- task_cputime_adjusted(current, &utime, &stime);
+ task_cputime(current, &utime, &stime);
accumulate_thread_rusage(p, r);
maxrss = p->signal->maxrss;
goto out;
@@ -1734,7 +1734,7 @@ static void k_getrusage(struct task_struct *p, int who, struct rusage *r)
break;
case RUSAGE_SELF:
- thread_group_cputime_adjusted(p, &tg_cputime);
+ thread_group_cputime(p, &tg_cputime);
utime += tg_cputime.utime;
stime += tg_cputime.stime;
r->ru_nvcsw += p->signal->nvcsw;
--
1.7.1
--
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