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sched: fix process time monotonicity
Spencer reported a problem where utime and stime were going negative despite
the fixes in commit b27f03d4bd
. The suspected
reason for the problem is that signal_struct maintains it's own utime and
stime (of exited tasks), these are not updated using the new task_utime()
routine, hence sig->utime can go backwards and cause the same problem
to occur (sig->utime, adds tsk->utime and not task_utime()). This patch
fixes the problem
TODO: using max(task->prev_utime, derived utime) works for now, but a more
generic solution is to implement cputime_max() and use the cputime_gt()
function for comparison.
Reported-by: spencer@bluehost.com
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
parent
56c7426b39
commit
49048622ea
@ -337,65 +337,6 @@ int proc_pid_status(struct seq_file *m, struct pid_namespace *ns,
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return 0;
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}
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/*
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* Use precise platform statistics if available:
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*/
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#ifdef CONFIG_VIRT_CPU_ACCOUNTING
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static cputime_t task_utime(struct task_struct *p)
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{
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return p->utime;
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}
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static cputime_t task_stime(struct task_struct *p)
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{
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return p->stime;
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}
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#else
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static cputime_t task_utime(struct task_struct *p)
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{
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clock_t utime = cputime_to_clock_t(p->utime),
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total = utime + cputime_to_clock_t(p->stime);
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u64 temp;
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/*
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* Use CFS's precise accounting:
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*/
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temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
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if (total) {
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temp *= utime;
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do_div(temp, total);
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}
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utime = (clock_t)temp;
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p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
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return p->prev_utime;
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}
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static cputime_t task_stime(struct task_struct *p)
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{
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clock_t stime;
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/*
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* Use CFS's precise accounting. (we subtract utime from
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* the total, to make sure the total observed by userspace
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* grows monotonically - apps rely on that):
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*/
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stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
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cputime_to_clock_t(task_utime(p));
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if (stime >= 0)
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p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
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return p->prev_stime;
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}
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#endif
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static cputime_t task_gtime(struct task_struct *p)
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{
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return p->gtime;
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}
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static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
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struct pid *pid, struct task_struct *task, int whole)
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{
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@ -1475,6 +1475,10 @@ static inline void put_task_struct(struct task_struct *t)
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__put_task_struct(t);
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}
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extern cputime_t task_utime(struct task_struct *p);
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extern cputime_t task_stime(struct task_struct *p);
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extern cputime_t task_gtime(struct task_struct *p);
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/*
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* Per process flags
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*/
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@ -112,9 +112,9 @@ static void __exit_signal(struct task_struct *tsk)
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* We won't ever get here for the group leader, since it
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* will have been the last reference on the signal_struct.
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*/
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sig->utime = cputime_add(sig->utime, tsk->utime);
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sig->stime = cputime_add(sig->stime, tsk->stime);
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sig->gtime = cputime_add(sig->gtime, tsk->gtime);
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sig->utime = cputime_add(sig->utime, task_utime(tsk));
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sig->stime = cputime_add(sig->stime, task_stime(tsk));
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sig->gtime = cputime_add(sig->gtime, task_gtime(tsk));
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sig->min_flt += tsk->min_flt;
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sig->maj_flt += tsk->maj_flt;
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sig->nvcsw += tsk->nvcsw;
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@ -4178,6 +4178,65 @@ void account_steal_time(struct task_struct *p, cputime_t steal)
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cpustat->steal = cputime64_add(cpustat->steal, tmp);
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}
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/*
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* Use precise platform statistics if available:
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*/
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#ifdef CONFIG_VIRT_CPU_ACCOUNTING
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cputime_t task_utime(struct task_struct *p)
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{
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return p->utime;
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}
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cputime_t task_stime(struct task_struct *p)
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{
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return p->stime;
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}
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#else
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cputime_t task_utime(struct task_struct *p)
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{
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clock_t utime = cputime_to_clock_t(p->utime),
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total = utime + cputime_to_clock_t(p->stime);
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u64 temp;
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/*
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* Use CFS's precise accounting:
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*/
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temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);
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if (total) {
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temp *= utime;
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do_div(temp, total);
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}
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utime = (clock_t)temp;
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p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime));
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return p->prev_utime;
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}
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cputime_t task_stime(struct task_struct *p)
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{
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clock_t stime;
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/*
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* Use CFS's precise accounting. (we subtract utime from
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* the total, to make sure the total observed by userspace
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* grows monotonically - apps rely on that):
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*/
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stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
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cputime_to_clock_t(task_utime(p));
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if (stime >= 0)
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p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime));
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return p->prev_stime;
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}
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#endif
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inline cputime_t task_gtime(struct task_struct *p)
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{
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return p->gtime;
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}
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/*
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* This function gets called by the timer code, with HZ frequency.
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* We call it with interrupts disabled.
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