From: Steven Rostedt <rostedt@goodmis.org> To: Petr Mladek <pmladek@suse.com> Cc: LKML <linux-kernel@vger.kernel.org>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@rostedt.homelinux.com Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Date: Fri, 22 Dec 2017 07:44:26 -0500 [thread overview] Message-ID: <20171222074426.5df24526@gandalf.local.home> (raw) In-Reply-To: <20171222102927.eiunret5ykx55bvq@pathway.suse.cz> On Fri, 22 Dec 2017 11:31:31 +0100 Petr Mladek <pmladek@suse.com> wrote: > > Index: linux-trace.git/kernel/printk/printk.c > > =================================================================== > > --- linux-trace.git.orig/kernel/printk/printk.c > > +++ linux-trace.git/kernel/printk/printk.c > > @@ -2141,6 +2196,7 @@ void console_unlock(void) > > static u64 seen_seq; > > unsigned long flags; > > bool wake_klogd = false; > > + bool waiter = false; > > bool do_cond_resched, retry; > > > > if (console_suspended) { > > @@ -2229,14 +2285,64 @@ skip: > > console_seq++; > > raw_spin_unlock(&logbuf_lock); > > > > + /* > > + * While actively printing out messages, if another printk() > > + * were to occur on another CPU, it may wait for this one to > > + * finish. This task can not be preempted if there is a > > + * waiter waiting to take over. > > + */ > > + raw_spin_lock(&console_owner_lock); > > + console_owner = current; > > + raw_spin_unlock(&console_owner_lock); > > One idea. We could do the above only when "do_cond_resched" is false. > I mean that we could allow stealing the console duty only from > atomic context. I'd like to hold off before making a change like that. I thought about it, but by saying "atomic" is more important than "non-atomic" can also lead to problems. Once you don't allow stealing, you just changed printk to be unbounded again. Maybe that's not an issue. But I'd rather add that as an enhancement in case. I could make this a patch series, and we can build cases like this up. > > If I get it correctly, this variable is always true in schedulable > context. > > > + > > + /* The waiter may spin on us after setting console_owner */ > > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > > + > > stop_critical_timings(); /* don't trace print latency */ > > call_console_drivers(ext_text, ext_len, text, len); > > start_critical_timings(); > > + > > + raw_spin_lock(&console_owner_lock); > > + waiter = READ_ONCE(console_waiter); > > + console_owner = NULL; > > + raw_spin_unlock(&console_owner_lock); > > + > > + /* > > + * If there is a waiter waiting for us, then pass the > > + * rest of the work load over to that waiter. > > + */ > > + if (waiter) > > + break; > > + > > + /* There was no waiter, and nothing will spin on us here */ > > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > > + > > printk_safe_exit_irqrestore(flags); > > > > if (do_cond_resched) > > cond_resched(); > > On the contrary, we could allow steeling the console semaphore > when sleeping here. It would allow to get the messages out > faster. It might help to move the duty to someone who is > actually producing many messages or even the panic() caller. Good point. I'll add a patch that adds that feature too. Thanks! -- Steve
WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org> To: Petr Mladek <pmladek@suse.com> Cc: LKML <linux-kernel@vger.kernel.org>, akpm@linux-foundation.org, linux-mm@kvack.org, Cong Wang <xiyou.wangcong@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Johannes Weiner <hannes@cmpxchg.org>, Mel Gorman <mgorman@suse.de>, Michal Hocko <mhocko@kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, rostedt@home.goodmis.org Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Date: Fri, 22 Dec 2017 07:44:26 -0500 [thread overview] Message-ID: <20171222074426.5df24526@gandalf.local.home> (raw) In-Reply-To: <20171222102927.eiunret5ykx55bvq@pathway.suse.cz> On Fri, 22 Dec 2017 11:31:31 +0100 Petr Mladek <pmladek@suse.com> wrote: > > Index: linux-trace.git/kernel/printk/printk.c > > =================================================================== > > --- linux-trace.git.orig/kernel/printk/printk.c > > +++ linux-trace.git/kernel/printk/printk.c > > @@ -2141,6 +2196,7 @@ void console_unlock(void) > > static u64 seen_seq; > > unsigned long flags; > > bool wake_klogd = false; > > + bool waiter = false; > > bool do_cond_resched, retry; > > > > if (console_suspended) { > > @@ -2229,14 +2285,64 @@ skip: > > console_seq++; > > raw_spin_unlock(&logbuf_lock); > > > > + /* > > + * While actively printing out messages, if another printk() > > + * were to occur on another CPU, it may wait for this one to > > + * finish. This task can not be preempted if there is a > > + * waiter waiting to take over. > > + */ > > + raw_spin_lock(&console_owner_lock); > > + console_owner = current; > > + raw_spin_unlock(&console_owner_lock); > > One idea. We could do the above only when "do_cond_resched" is false. > I mean that we could allow stealing the console duty only from > atomic context. I'd like to hold off before making a change like that. I thought about it, but by saying "atomic" is more important than "non-atomic" can also lead to problems. Once you don't allow stealing, you just changed printk to be unbounded again. Maybe that's not an issue. But I'd rather add that as an enhancement in case. I could make this a patch series, and we can build cases like this up. > > If I get it correctly, this variable is always true in schedulable > context. > > > + > > + /* The waiter may spin on us after setting console_owner */ > > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > > + > > stop_critical_timings(); /* don't trace print latency */ > > call_console_drivers(ext_text, ext_len, text, len); > > start_critical_timings(); > > + > > + raw_spin_lock(&console_owner_lock); > > + waiter = READ_ONCE(console_waiter); > > + console_owner = NULL; > > + raw_spin_unlock(&console_owner_lock); > > + > > + /* > > + * If there is a waiter waiting for us, then pass the > > + * rest of the work load over to that waiter. > > + */ > > + if (waiter) > > + break; > > + > > + /* There was no waiter, and nothing will spin on us here */ > > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > > + > > printk_safe_exit_irqrestore(flags); > > > > if (do_cond_resched) > > cond_resched(); > > On the contrary, we could allow steeling the console semaphore > when sleeping here. It would allow to get the messages out > faster. It might help to move the duty to someone who is > actually producing many messages or even the panic() caller. Good point. I'll add a patch that adds that feature too. Thanks! -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-12-22 12:44 UTC|newest] Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-11-08 15:27 [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt 2017-11-08 15:27 ` Steven Rostedt 2017-11-09 10:12 ` Michal Hocko 2017-11-09 10:12 ` Michal Hocko 2017-11-09 10:22 ` [PATCH v4] printk: Add console owner and waiter logic to loadbalance " Tetsuo Handa 2017-11-09 10:22 ` Tetsuo Handa 2017-11-09 10:26 ` Michal Hocko 2017-11-09 10:26 ` Michal Hocko 2017-11-09 11:03 ` Tetsuo Handa 2017-11-09 11:03 ` Tetsuo Handa 2017-11-09 11:31 ` Michal Hocko 2017-11-09 11:31 ` Michal Hocko 2017-11-09 12:07 ` Tetsuo Handa 2017-11-09 12:07 ` Tetsuo Handa 2017-11-24 15:54 ` [PATCH v4] printk: Add console owner and waiter logic to load balance " Petr Mladek 2017-11-24 15:54 ` Petr Mladek 2017-11-24 15:58 ` Petr Mladek 2017-11-24 15:58 ` Petr Mladek 2017-11-27 8:53 ` Byungchul Park 2017-11-27 8:53 ` Byungchul Park 2017-11-28 1:42 ` Byungchul Park 2017-11-28 1:42 ` Byungchul Park 2017-12-08 14:00 ` Petr Mladek 2017-12-08 14:00 ` Petr Mladek 2017-12-12 5:39 ` Sergey Senozhatsky 2017-12-12 5:39 ` Sergey Senozhatsky 2017-12-12 19:27 ` Steven Rostedt 2017-12-12 19:27 ` Steven Rostedt 2017-12-13 1:50 ` Sergey Senozhatsky 2017-12-13 1:50 ` Sergey Senozhatsky 2017-12-14 14:34 ` Petr Mladek 2017-12-14 14:34 ` Petr Mladek 2017-12-14 13:51 ` Petr Mladek 2017-12-14 13:51 ` Petr Mladek 2017-11-27 8:48 ` Byungchul Park 2017-11-27 8:48 ` Byungchul Park 2017-11-28 6:23 ` Sergey Senozhatsky 2017-11-28 6:23 ` Sergey Senozhatsky 2017-12-22 10:31 ` Petr Mladek 2017-12-22 10:31 ` Petr Mladek 2017-12-22 12:44 ` Steven Rostedt [this message] 2017-12-22 12:44 ` Steven Rostedt 2018-01-10 12:50 ` Petr Mladek 2018-01-10 12:50 ` Petr Mladek -- strict thread matches above, loose matches on Subject: below -- 2017-11-08 15:13 Steven Rostedt 2017-11-08 15:03 Steven Rostedt 2017-11-08 15:10 ` Steven Rostedt
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