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Message-ID: <20140814174849.GA5091@redhat.com> Date: Thu, 14 Aug 2014 19:48:49 +0200 From: Oleg Nesterov <oleg@...hat.com> To: Rik van Riel <riel@...hat.com> Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>, Frank Mayhar <fmayhar@...gle.com>, Frederic Weisbecker <fweisbec@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, Sanjay Rao <srao@...hat.com>, Larry Woodman <lwoodman@...hat.com> Subject: Re: [PATCH RFC] time,signal: protect resource use statistics with seqlock On 08/14, Oleg Nesterov wrote: > > OK, lets forget about alternative approach for now. We can reconsider > it later. At least I have to admit that seqlock is more straighforward. Yes. But just for record, the "lockless" version doesn't look that bad to me, void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times) { struct signal_struct *sig = tsk->signal; bool lockless, is_dead; struct task_struct *t; unsigned long flags; u64 exec; lockless = true; is_dead = !lock_task_sighand(p, &flags); retry: times->utime = sig->utime; times->stime = sig->stime; times->sum_exec_runtime = exec = sig->sum_sched_runtime; if (is_dead) return; if (lockless) unlock_task_sighand(p, &flags); rcu_read_lock(); for_each_thread(tsk, t) { cputime_t utime, stime; task_cputime(t, &utime, &stime); times->utime += utime; times->stime += stime; times->sum_exec_runtime += task_sched_runtime(t); } rcu_read_unlock(); if (lockless) { lockless = false; is_dead = !lock_task_sighand(p, &flags); if (is_dead || exec != sig->sum_sched_runtime) goto retry; } unlock_task_sighand(p, &flags); } The obvious problem is that we should shift lock_task_sighand() from the callers to thread_group_cputime() first, or add thread_group_cputime_lockless() and change the current users one by one. And of course, stats_lock is more generic. Oleg. -- 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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