Messages in this thread | | | Date | Wed, 13 Aug 2014 19:40:48 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH RFC] time: drop do_sys_times spinlock |
| |
On Wed, Aug 13, 2014 at 07:22:30PM +0200, Oleg Nesterov wrote: > On 08/12, Rik van Riel wrote: > > > > Any other ideas? > > To simplify, lets suppose that we only need sum_exec_runtime. > > Perhaps we can do something like this > > u64 thread_group_sched_runtime(void) > { > struct task_struct *tsk = current; > spinlock_t *siglock = &tsk->sighand->siglock; /* stable */ > struct task_struct *t; > u64 x1, x2; > > retry: > x1 = tsk->signal->sum_sched_runtime; > rmb(); > spin_unlock_wait(siglock); > rmb(); > > x2 = 0; > rcu_read_lock(); > for_each_thread(tsk, t) > x2 += task_sched_runtime(t); > rcu_read_unlock(); > > rmb(); > spin_unlock_wait(siglock); > rmb(); > > if (x1 != tsk->signal->sum_sched_runtime) > goto retry; > > return x1 + x2; > } > > ? > > We do not care if for_each_thread() misses the new thread, we can pretend > thread_group_sched_runtime() was called before clone. > > We do not care if a thread with sum_sched_runtime == 0 exits, obviously. > > Otherwise "x1 != tsk->signal->sum_sched_runtime" should tell us that we > raced with __exit_signal().
So the problem with the above is the lack of fwd progress; if there's enough clone()/exit() happening in the thread group (and the more CPUs the more possible), we'll keep repeating.
[unhandled content-type:application/pgp-signature] | |