Messages in this thread Patch in this message | | | Date | Sat, 30 Aug 2008 19:25:57 +0530 | From | Balbir Singh <> | Subject | Re: Still seeing decreasing stime/utime |
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* Peter Zijlstra <a.p.zijlstra@chello.nl> [2008-08-30 13:27:36]:
> On Sat, 2008-08-30 at 11:26 +0530, Balbir Singh wrote: > > Spencer Candland wrote: > > >> Here is an experimental patch (I've just compiled and booted a machine > > >> with it, I am unable to reproduce your problem), could you please test > > >> it for me and see if it helps solve the problem > > > > > > Looks like this fixed it. I have been testing this for the last 16 > > > hours and everything is looking good. > > > > > > > Excellent! Ingo, Peter, do you like the patch? If so, could you please pick it > > up Ingo. I think we should even push the fix to stable releases. > > Looks good, except for the issue you yourself earlier raised, a few of > those functions looks too large to be inlined. >
Here's the updated revision with task_*time functions moved to sched.c and inlining removed, except for task_gtime(). I've compiled and booted a machine (x86_64) with this patch applied.
Reported-by: spencer@bluehost.com
Spencer reported a problem where utime and stime were going negative despite the fixes in commit b27f03d4bdc145a09fb7b0c0e004b29f1ee555fa. 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.
Comments?
Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com> ---
fs/proc/array.c | 59 -------------------------------------------------- include/linux/sched.h | 4 +++ kernel/exit.c | 6 ++--- kernel/sched.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 66 insertions(+), 62 deletions(-)
diff -puN kernel/exit.c~fix-utime-stime-moving-backwards kernel/exit.c --- linux-2.6.27-rc3/kernel/exit.c~fix-utime-stime-moving-backwards 2008-08-29 03:14:57.000000000 +0530 +++ linux-2.6.27-rc3-balbir/kernel/exit.c 2008-08-29 03:21:18.000000000 +0530 @@ -115,9 +115,9 @@ static void __exit_signal(struct task_st * We won't ever get here for the group leader, since it * will have been the last reference on the signal_struct. */ - sig->utime = cputime_add(sig->utime, tsk->utime); - sig->stime = cputime_add(sig->stime, tsk->stime); - sig->gtime = cputime_add(sig->gtime, tsk->gtime); + sig->utime = cputime_add(sig->utime, task_utime(tsk)); + sig->stime = cputime_add(sig->stime, task_stime(tsk)); + sig->gtime = cputime_add(sig->gtime, task_gtime(tsk)); sig->min_flt += tsk->min_flt; sig->maj_flt += tsk->maj_flt; sig->nvcsw += tsk->nvcsw; diff -puN fs/proc/array.c~fix-utime-stime-moving-backwards fs/proc/array.c --- linux-2.6.27-rc3/fs/proc/array.c~fix-utime-stime-moving-backwards 2008-08-29 03:14:58.000000000 +0530 +++ linux-2.6.27-rc3-balbir/fs/proc/array.c 2008-08-29 03:16:09.000000000 +0530 @@ -349,65 +349,6 @@ int proc_pid_status(struct seq_file *m, return 0; } -/* - * Use precise platform statistics if available: - */ -#ifdef CONFIG_VIRT_CPU_ACCOUNTING -static cputime_t task_utime(struct task_struct *p) -{ - return p->utime; -} - -static cputime_t task_stime(struct task_struct *p) -{ - return p->stime; -} -#else -static cputime_t task_utime(struct task_struct *p) -{ - clock_t utime = cputime_to_clock_t(p->utime), - total = utime + cputime_to_clock_t(p->stime); - u64 temp; - - /* - * Use CFS's precise accounting: - */ - temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime); - - if (total) { - temp *= utime; - do_div(temp, total); - } - utime = (clock_t)temp; - - p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime)); - return p->prev_utime; -} - -static cputime_t task_stime(struct task_struct *p) -{ - clock_t stime; - - /* - * Use CFS's precise accounting. (we subtract utime from - * the total, to make sure the total observed by userspace - * grows monotonically - apps rely on that): - */ - stime = nsec_to_clock_t(p->se.sum_exec_runtime) - - cputime_to_clock_t(task_utime(p)); - - if (stime >= 0) - p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime)); - - return p->prev_stime; -} -#endif - -static cputime_t task_gtime(struct task_struct *p) -{ - return p->gtime; -} - static int do_task_stat(struct seq_file *m, struct pid_namespace *ns, struct pid *pid, struct task_struct *task, int whole) { diff -puN include/linux/sched.h~fix-utime-stime-moving-backwards include/linux/sched.h --- linux-2.6.27-rc3/include/linux/sched.h~fix-utime-stime-moving-backwards 2008-08-29 03:14:58.000000000 +0530 +++ linux-2.6.27-rc3-balbir/include/linux/sched.h 2008-08-30 18:43:56.000000000 +0530 @@ -1430,6 +1430,10 @@ static inline void put_task_struct(struc __put_task_struct(t); } +extern cputime_t task_utime(struct task_struct *p); +extern cputime_t task_stime(struct task_struct *p); +extern cputime_t task_gtime(struct task_struct *p); + /* * Per process flags */ diff -puN kernel/sched.c~fix-utime-stime-moving-backwards kernel/sched.c --- linux-2.6.27-rc3/kernel/sched.c~fix-utime-stime-moving-backwards 2008-08-30 18:38:15.000000000 +0530 +++ linux-2.6.27-rc3-balbir/kernel/sched.c 2008-08-30 18:41:40.000000000 +0530 @@ -4176,6 +4176,65 @@ void account_steal_time(struct task_stru } /* + * Use precise platform statistics if available: + */ +#ifdef CONFIG_VIRT_CPU_ACCOUNTING +cputime_t task_utime(struct task_struct *p) +{ + return p->utime; +} + +cputime_t task_stime(struct task_struct *p) +{ + return p->stime; +} +#else +cputime_t task_utime(struct task_struct *p) +{ + clock_t utime = cputime_to_clock_t(p->utime), + total = utime + cputime_to_clock_t(p->stime); + u64 temp; + + /* + * Use CFS's precise accounting: + */ + temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime); + + if (total) { + temp *= utime; + do_div(temp, total); + } + utime = (clock_t)temp; + + p->prev_utime = max(p->prev_utime, clock_t_to_cputime(utime)); + return p->prev_utime; +} + +cputime_t task_stime(struct task_struct *p) +{ + clock_t stime; + + /* + * Use CFS's precise accounting. (we subtract utime from + * the total, to make sure the total observed by userspace + * grows monotonically - apps rely on that): + */ + stime = nsec_to_clock_t(p->se.sum_exec_runtime) - + cputime_to_clock_t(task_utime(p)); + + if (stime >= 0) + p->prev_stime = max(p->prev_stime, clock_t_to_cputime(stime)); + + return p->prev_stime; +} +#endif + +inline cputime_t task_gtime(struct task_struct *p) +{ + return p->gtime; +} + +/* * This function gets called by the timer code, with HZ frequency. * We call it with interrupts disabled. * _ -- Balbir
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