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Date: Thu, 12 Nov 2009 15:49:20 +0100 From: Stanislaw Gruszka <sgruszka@...hat.com> To: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> Cc: Américo Wang <xiyou.wangcong@...il.com>, Peter Zijlstra <peterz@...radead.org>, Spencer Candland <spencer@...ehost.com>, linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>, Oleg Nesterov <oleg@...hat.com> Subject: Re: [PATCH] fix granularity of task_u/stime(), v2 Hi On Thu, Nov 12, 2009 at 01:33:45PM +0900, Hidetoshi Seto wrote: > Originally task_s/utime() were designed to return clock_t but later > changed to return cputime_t by following commit: > > commit efe567fc8281661524ffa75477a7c4ca9b466c63 > Author: Christian Borntraeger <borntraeger@...ibm.com> > Date: Thu Aug 23 15:18:02 2007 +0200 > > It only changed the type of return value, but not the implementation. > As the result the granularity of task_s/utime() is still that of > clock_t, not that of cputime_t. > > So using task_s/utime() in __exit_signal() makes values accumulated > to the signal struct to be rounded and coarse grained. > > This patch removes casts to clock_t in task_u/stime(), to keep > granularity of cputime_t over the calculation. > > v2: > Use div_u64() to avoid error "undefined reference to `__udivdi3`" > on some 32bit systems. > > Signed-off-by: Hidetoshi Seto <seto.hidetoshi@...fujitsu.com> > --- > kernel/sched.c | 22 +++++++++++++--------- > 1 files changed, 13 insertions(+), 9 deletions(-) Patch not fix the issue on my system. I test it alone, together with posix-cpu-timers: avoid do_sys_times() races with __exit_signal( and (further) together with --- a/kernel/posix-cpu-timers.c +++ b/kernel/posix-cpu-timers.c @@ -248,8 +248,8 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times) t = tsk; do { - times->utime = cputime_add(times->utime, t->utime); - times->stime = cputime_add(times->stime, t->stime); + times->utime = cputime_add(times->utime, task_utime(t)); + times->stime = cputime_add(times->stime, task_stime(t)); times->sum_exec_runtime += t->se.sum_exec_runtime; t = next_thread(t); What only changed was probability to enter the issue. I can not reproduce the bug with below patch: diff --git a/kernel/exit.c b/kernel/exit.c index f7864ac..b85e384 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -110,8 +110,8 @@ static void __exit_signal(struct task_struct *tsk) * 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, task_utime(tsk)); - sig->stime = cputime_add(sig->stime, task_stime(tsk)); + sig->utime = cputime_add(sig->utime, tsk->utime); //task_utime(tsk)); + sig->stime = cputime_add(sig->stime, tsk->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; diff --git a/kernel/sys.c b/kernel/sys.c index ce17760..8be5b75 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -914,8 +914,8 @@ void do_sys_times(struct tms *tms) struct task_cputime cputime; cputime_t cutime, cstime; - thread_group_cputime(current, &cputime); spin_lock_irq(¤t->sighand->siglock); + thread_group_cputime(current, &cputime); cutime = current->signal->cutime; cstime = current->signal->cstime; spin_unlock_irq(¤t->sighand->siglock); Perhaps we can remove task_{u,s}time() in some places or maybe at whole ? Stanislaw -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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