From: Steven Rostedt <rostedt@goodmis.org> To: Byungchul Park <byungchul.park@lge.com> Cc: Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, 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>, 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, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Tejun Heo <tj@kernel.org>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes Date: Wed, 17 Jan 2018 21:19:53 -0500 [thread overview] Message-ID: <20180117211953.2403d189@vmware.local.home> (raw) In-Reply-To: <4a24ce1d-a606-3add-ec30-91ce9a1a1281@lge.com> On Thu, 18 Jan 2018 10:53:37 +0900 Byungchul Park <byungchul.park@lge.com> wrote: > Hello, > > This is a thing simulating a wait for an event e.g. > wait_for_completion() doing spinning instead of sleep, rather > than a spinlock. I mean: > > This context > ------------ > while (READ_ONCE(console_waiter)) /* Wait for the event */ > cpu_relax(); > > Another context > --------------- > WRITE_ONCE(console_waiter, false); /* Event */ I disagree. It is like a spinlock. You can say a spinlock() that is blocked is also waiting for an event. That event being the owner does a spin_unlock(). > > That's why I said this's the exact case of cross-release. Anyway > without cross-release, we usually use typical acquire/release > pairs to cover a wait for an event in the following way: > > A context > --------- > lock_map_acquire(wait); /* Or lock_map_acquire_read(wait) */ > /* Read one is better though.. */ > > /* A section, we suspect, a wait for an event might happen. */ > ... > lock_map_release(wait); > > > The place actually doing the wait > --------------------------------- > lock_map_acquire(wait); > lock_map_acquire(wait); > > wait_for_event(wait); /* Actually do the wait */ > > You can see a simple example of how to use them by searching > kernel/cpu.c with "lock_acquire" and "wait_for_completion". > > However, as I said, if you suspect that cpu_relax() includes > the wait, then it's ok to leave it. Otherwise, I think it > would be better to change it in the way I showed you above. I find your way confusing. I'm simulating a spinlock not a wait for completion. A wait for completion usually initiates something then waits for it to complete. This is trying to get into a critical area but another task is currently in it. It's simulating a spinlock as far as I can see. -- Steve
WARNING: multiple messages have this Message-ID (diff)
From: Steven Rostedt <rostedt@goodmis.org> To: Byungchul Park <byungchul.park@lge.com> Cc: Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, 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>, 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, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Tejun Heo <tj@kernel.org>, Pavel Machek <pavel@ucw.cz>, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes Date: Wed, 17 Jan 2018 21:19:53 -0500 [thread overview] Message-ID: <20180117211953.2403d189@vmware.local.home> (raw) In-Reply-To: <4a24ce1d-a606-3add-ec30-91ce9a1a1281@lge.com> On Thu, 18 Jan 2018 10:53:37 +0900 Byungchul Park <byungchul.park@lge.com> wrote: > Hello, > > This is a thing simulating a wait for an event e.g. > wait_for_completion() doing spinning instead of sleep, rather > than a spinlock. I mean: > > This context > ------------ > while (READ_ONCE(console_waiter)) /* Wait for the event */ > cpu_relax(); > > Another context > --------------- > WRITE_ONCE(console_waiter, false); /* Event */ I disagree. It is like a spinlock. You can say a spinlock() that is blocked is also waiting for an event. That event being the owner does a spin_unlock(). > > That's why I said this's the exact case of cross-release. Anyway > without cross-release, we usually use typical acquire/release > pairs to cover a wait for an event in the following way: > > A context > --------- > lock_map_acquire(wait); /* Or lock_map_acquire_read(wait) */ > /* Read one is better though.. */ > > /* A section, we suspect, a wait for an event might happen. */ > ... > lock_map_release(wait); > > > The place actually doing the wait > --------------------------------- > lock_map_acquire(wait); > lock_map_acquire(wait); > > wait_for_event(wait); /* Actually do the wait */ > > You can see a simple example of how to use them by searching > kernel/cpu.c with "lock_acquire" and "wait_for_completion". > > However, as I said, if you suspect that cpu_relax() includes > the wait, then it's ok to leave it. Otherwise, I think it > would be better to change it in the way I showed you above. I find your way confusing. I'm simulating a spinlock not a wait for completion. A wait for completion usually initiates something then waits for it to complete. This is trying to get into a critical area but another task is currently in it. It's simulating a spinlock as far as I can see. -- 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:[~2018-01-18 2:20 UTC|newest] Thread overview: 280+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-01-10 13:24 [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 13:24 ` [PATCH v5 1/2] printk: Add console owner and waiter logic to load balance console writes Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 16:50 ` Steven Rostedt 2018-01-10 16:50 ` Steven Rostedt 2018-01-12 16:54 ` Steven Rostedt 2018-01-12 16:54 ` Steven Rostedt 2018-01-12 17:11 ` Steven Rostedt 2018-01-12 17:11 ` Steven Rostedt 2018-01-17 19:13 ` Rasmus Villemoes 2018-01-17 19:13 ` Rasmus Villemoes 2018-01-17 19:33 ` Steven Rostedt 2018-01-17 19:33 ` Steven Rostedt 2018-01-19 9:51 ` Sergey Senozhatsky 2018-01-19 9:51 ` Sergey Senozhatsky 2018-01-18 22:03 ` Pavel Machek 2018-01-18 22:03 ` Pavel Machek 2018-01-19 0:20 ` Steven Rostedt 2018-01-19 0:20 ` Steven Rostedt 2018-01-17 2:19 ` Byungchul Park 2018-01-17 2:19 ` Byungchul Park 2018-01-17 4:54 ` Byungchul Park 2018-01-17 4:54 ` Byungchul Park 2018-01-17 7:34 ` Byungchul Park 2018-01-17 7:34 ` Byungchul Park 2018-01-17 12:04 ` Petr Mladek 2018-01-17 12:04 ` Petr Mladek 2018-01-18 1:53 ` Byungchul Park 2018-01-18 1:53 ` Byungchul Park 2018-01-18 1:57 ` Byungchul Park 2018-01-18 1:57 ` Byungchul Park 2018-01-18 2:19 ` Steven Rostedt [this message] 2018-01-18 2:19 ` Steven Rostedt 2018-01-18 4:01 ` Byungchul Park 2018-01-18 4:01 ` Byungchul Park 2018-01-18 15:21 ` Steven Rostedt 2018-01-18 15:21 ` Steven Rostedt 2018-01-19 2:37 ` Byungchul Park 2018-01-19 2:37 ` Byungchul Park 2018-01-19 3:27 ` Steven Rostedt 2018-01-19 3:27 ` Steven Rostedt 2018-01-22 2:31 ` Byungchul Park 2018-01-22 2:31 ` Byungchul Park 2018-01-10 13:24 ` [PATCH v5 2/2] printk: Hide console waiter logic into helpers Petr Mladek 2018-01-10 13:24 ` Petr Mladek 2018-01-10 17:52 ` Steven Rostedt 2018-01-10 17:52 ` Steven Rostedt 2018-01-11 12:03 ` Petr Mladek 2018-01-11 12:03 ` Petr Mladek 2018-01-12 15:37 ` Steven Rostedt 2018-01-12 15:37 ` Steven Rostedt 2018-01-12 16:08 ` Petr Mladek 2018-01-12 16:08 ` Petr Mladek 2018-01-12 16:36 ` Steven Rostedt 2018-01-12 16:36 ` Steven Rostedt 2018-01-15 16:08 ` Petr Mladek 2018-01-15 16:08 ` Petr Mladek 2018-01-16 5:05 ` Sergey Senozhatsky 2018-01-16 5:05 ` Sergey Senozhatsky 2018-01-10 14:05 ` [PATCH v5 0/2] printk: Console owner and waiter logic cleanup Tejun Heo 2018-01-10 14:05 ` Tejun Heo 2018-01-10 16:29 ` Petr Mladek 2018-01-10 16:29 ` Petr Mladek 2018-01-10 17:02 ` Tejun Heo 2018-01-10 17:02 ` Tejun Heo 2018-01-10 18:21 ` Peter Zijlstra 2018-01-10 18:21 ` Peter Zijlstra 2018-01-10 18:30 ` Tejun Heo 2018-01-10 18:30 ` Tejun Heo 2018-01-10 18:41 ` Peter Zijlstra 2018-01-10 18:41 ` Peter Zijlstra 2018-01-10 19:05 ` Tejun Heo 2018-01-10 19:05 ` Tejun Heo 2018-01-11 5:15 ` Sergey Senozhatsky 2018-01-11 5:15 ` Sergey Senozhatsky 2018-01-10 18:22 ` Steven Rostedt 2018-01-10 18:22 ` Steven Rostedt 2018-01-10 18:36 ` Tejun Heo 2018-01-10 18:36 ` Tejun Heo 2018-01-10 18:40 ` Mathieu Desnoyers 2018-01-10 18:40 ` Mathieu Desnoyers 2018-01-11 7:36 ` Sergey Senozhatsky 2018-01-11 7:36 ` Sergey Senozhatsky 2018-01-11 11:24 ` Petr Mladek 2018-01-11 11:24 ` Petr Mladek 2018-01-11 13:19 ` Sergey Senozhatsky 2018-01-11 13:19 ` Sergey Senozhatsky 2018-01-24 9:36 ` Peter Zijlstra 2018-01-24 9:36 ` Peter Zijlstra 2018-01-24 18:46 ` Tejun Heo 2018-01-24 18:46 ` Tejun Heo 2018-05-09 8:58 ` Sergey Senozhatsky 2018-05-09 8:58 ` Sergey Senozhatsky 2018-01-10 18:54 ` Steven Rostedt 2018-01-10 18:54 ` Steven Rostedt 2018-01-11 5:10 ` Sergey Senozhatsky 2018-01-11 5:10 ` Sergey Senozhatsky 2018-01-10 18:05 ` Steven Rostedt 2018-01-10 18:05 ` Steven Rostedt 2018-01-10 18:12 ` Tejun Heo 2018-01-10 18:12 ` Tejun Heo 2018-01-10 18:14 ` Tejun Heo 2018-01-10 18:14 ` Tejun Heo 2018-01-10 18:45 ` Steven Rostedt 2018-01-10 18:45 ` Steven Rostedt 2018-01-10 18:41 ` Steven Rostedt 2018-01-10 18:41 ` Steven Rostedt 2018-01-10 18:57 ` Tejun Heo 2018-01-10 18:57 ` Tejun Heo 2018-01-10 19:17 ` Steven Rostedt 2018-01-10 19:17 ` Steven Rostedt 2018-01-10 19:34 ` Tejun Heo 2018-01-10 19:34 ` Tejun Heo 2018-01-10 19:44 ` Steven Rostedt 2018-01-10 19:44 ` Steven Rostedt 2018-01-10 22:44 ` Tejun Heo 2018-01-10 22:44 ` Tejun Heo 2018-01-11 5:35 ` Sergey Senozhatsky 2018-01-11 5:35 ` Sergey Senozhatsky 2018-01-11 4:58 ` Sergey Senozhatsky 2018-01-11 4:58 ` Sergey Senozhatsky 2018-01-11 9:34 ` Petr Mladek 2018-01-11 9:34 ` Petr Mladek 2018-01-11 10:38 ` Sergey Senozhatsky 2018-01-11 10:38 ` Sergey Senozhatsky 2018-01-11 11:50 ` Petr Mladek 2018-01-11 11:50 ` Petr Mladek 2018-01-11 16:29 ` Steven Rostedt 2018-01-11 16:29 ` Steven Rostedt 2018-01-12 1:30 ` Steven Rostedt 2018-01-12 1:30 ` Steven Rostedt 2018-01-12 2:55 ` Steven Rostedt 2018-01-12 2:55 ` Steven Rostedt 2018-01-12 4:20 ` Steven Rostedt 2018-01-12 4:20 ` Steven Rostedt 2018-01-16 19:44 ` Tejun Heo 2018-01-16 19:44 ` Tejun Heo 2018-01-17 9:12 ` Petr Mladek 2018-01-17 9:12 ` Petr Mladek 2018-01-17 15:15 ` Tejun Heo 2018-01-17 15:15 ` Tejun Heo 2018-01-17 17:12 ` Steven Rostedt 2018-01-17 17:12 ` Steven Rostedt 2018-01-17 18:42 ` Steven Rostedt 2018-01-17 18:42 ` Steven Rostedt 2018-01-19 18:20 ` Steven Rostedt 2018-01-19 18:20 ` Steven Rostedt 2018-01-20 7:14 ` Sergey Senozhatsky 2018-01-20 7:14 ` Sergey Senozhatsky 2018-01-20 15:49 ` Steven Rostedt 2018-01-20 15:49 ` Steven Rostedt 2018-01-21 14:15 ` Sergey Senozhatsky 2018-01-21 14:15 ` Sergey Senozhatsky 2018-01-21 21:04 ` Steven Rostedt 2018-01-21 21:04 ` Steven Rostedt 2018-01-22 8:56 ` Sergey Senozhatsky 2018-01-22 8:56 ` Sergey Senozhatsky 2018-01-22 10:28 ` Sergey Senozhatsky 2018-01-22 10:28 ` Sergey Senozhatsky 2018-01-22 10:36 ` Sergey Senozhatsky 2018-01-22 10:36 ` Sergey Senozhatsky 2018-01-23 6:40 ` Sergey Senozhatsky 2018-01-23 6:40 ` Sergey Senozhatsky 2018-01-23 7:05 ` Sergey Senozhatsky 2018-01-23 7:05 ` Sergey Senozhatsky 2018-01-23 7:31 ` Sergey Senozhatsky 2018-01-23 7:31 ` Sergey Senozhatsky 2018-01-23 14:56 ` Steven Rostedt 2018-01-23 14:56 ` Steven Rostedt 2018-01-23 15:21 ` Sergey Senozhatsky 2018-01-23 15:21 ` Sergey Senozhatsky 2018-01-23 15:41 ` Steven Rostedt 2018-01-23 15:41 ` Steven Rostedt 2018-01-23 15:43 ` Tejun Heo 2018-01-23 15:43 ` Tejun Heo 2018-01-23 16:12 ` Sergey Senozhatsky 2018-01-23 16:12 ` Sergey Senozhatsky 2018-01-23 16:13 ` Steven Rostedt 2018-01-23 16:13 ` Steven Rostedt 2018-01-23 17:21 ` Tejun Heo 2018-01-23 17:21 ` Tejun Heo 2018-04-23 5:35 ` Sergey Senozhatsky 2018-04-23 5:35 ` Sergey Senozhatsky 2018-01-23 16:01 ` Sergey Senozhatsky 2018-01-23 16:01 ` Sergey Senozhatsky 2018-01-23 16:24 ` Steven Rostedt 2018-01-23 16:24 ` Steven Rostedt 2018-01-24 2:11 ` Sergey Senozhatsky 2018-01-24 2:11 ` Sergey Senozhatsky 2018-01-24 2:52 ` Steven Rostedt 2018-01-24 2:52 ` Steven Rostedt 2018-01-24 4:44 ` Sergey Senozhatsky 2018-01-24 4:44 ` Sergey Senozhatsky 2018-01-23 17:22 ` Tejun Heo 2018-01-23 17:22 ` Tejun Heo 2018-01-20 12:19 ` Tejun Heo 2018-01-20 12:19 ` Tejun Heo 2018-01-20 14:51 ` Steven Rostedt 2018-01-20 14:51 ` Steven Rostedt 2018-01-17 20:05 ` Tejun Heo 2018-01-17 20:05 ` Tejun Heo 2018-01-18 5:43 ` Sergey Senozhatsky 2018-01-18 5:43 ` Sergey Senozhatsky 2018-01-18 11:51 ` Petr Mladek 2018-01-18 11:51 ` Petr Mladek 2018-01-18 5:42 ` Sergey Senozhatsky 2018-01-18 5:42 ` Sergey Senozhatsky 2018-01-12 3:12 ` Sergey Senozhatsky 2018-01-12 3:12 ` Sergey Senozhatsky 2018-01-12 2:56 ` Sergey Senozhatsky 2018-01-12 2:56 ` Sergey Senozhatsky 2018-01-12 3:21 ` Steven Rostedt 2018-01-12 3:21 ` Steven Rostedt 2018-01-12 10:05 ` Sergey Senozhatsky 2018-01-12 10:05 ` Sergey Senozhatsky 2018-01-12 12:21 ` Steven Rostedt 2018-01-12 12:21 ` Steven Rostedt 2018-01-12 12:55 ` Petr Mladek 2018-01-12 12:55 ` Petr Mladek 2018-01-13 7:31 ` Sergey Senozhatsky 2018-01-13 7:31 ` Sergey Senozhatsky 2018-01-15 8:51 ` Petr Mladek 2018-01-15 8:51 ` Petr Mladek 2018-01-15 9:48 ` Sergey Senozhatsky 2018-01-15 9:48 ` Sergey Senozhatsky 2018-01-16 5:16 ` Sergey Senozhatsky 2018-01-16 5:16 ` Sergey Senozhatsky 2018-01-16 9:08 ` Petr Mladek 2018-01-16 9:08 ` Petr Mladek 2018-01-15 12:08 ` Steven Rostedt 2018-01-15 12:08 ` Steven Rostedt 2018-01-16 4:51 ` Sergey Senozhatsky 2018-01-16 4:51 ` Sergey Senozhatsky 2018-01-13 7:28 ` Sergey Senozhatsky 2018-01-13 7:28 ` Sergey Senozhatsky 2018-01-15 10:17 ` Petr Mladek 2018-01-15 10:17 ` Petr Mladek 2018-01-15 11:50 ` Petr Mladek 2018-01-15 11:50 ` Petr Mladek 2018-01-16 6:10 ` Sergey Senozhatsky 2018-01-16 6:10 ` Sergey Senozhatsky 2018-01-16 9:36 ` Petr Mladek 2018-01-16 9:36 ` Petr Mladek 2018-01-16 10:10 ` Sergey Senozhatsky 2018-01-16 10:10 ` Sergey Senozhatsky 2018-01-16 16:06 ` Steven Rostedt 2018-01-16 16:06 ` Steven Rostedt 2018-01-16 5:23 ` Sergey Senozhatsky 2018-01-16 5:23 ` Sergey Senozhatsky 2018-01-15 12:06 ` Steven Rostedt 2018-01-15 12:06 ` Steven Rostedt 2018-01-15 14:45 ` Petr Mladek 2018-01-15 14:45 ` Petr Mladek 2018-01-16 2:23 ` Sergey Senozhatsky 2018-01-16 2:23 ` Sergey Senozhatsky 2018-01-16 4:47 ` Sergey Senozhatsky 2018-01-16 4:47 ` Sergey Senozhatsky 2018-01-16 10:19 ` Petr Mladek 2018-01-16 10:19 ` Petr Mladek 2018-01-17 2:24 ` Sergey Senozhatsky 2018-01-17 2:24 ` Sergey Senozhatsky 2018-01-16 15:45 ` Steven Rostedt 2018-01-16 15:45 ` Steven Rostedt 2018-01-17 2:18 ` Sergey Senozhatsky 2018-01-17 2:18 ` Sergey Senozhatsky 2018-01-17 13:04 ` Petr Mladek 2018-01-17 13:04 ` Petr Mladek 2018-01-17 15:24 ` Steven Rostedt 2018-01-17 15:24 ` Steven Rostedt 2018-01-18 4:31 ` Sergey Senozhatsky 2018-01-18 4:31 ` Sergey Senozhatsky 2018-01-18 15:22 ` Steven Rostedt 2018-01-18 15:22 ` Steven Rostedt 2018-01-16 10:13 ` Petr Mladek 2018-01-16 10:13 ` Petr Mladek 2018-01-17 6:29 ` Sergey Senozhatsky 2018-01-17 6:29 ` Sergey Senozhatsky 2018-01-16 1:46 ` Sergey Senozhatsky 2018-01-16 1:46 ` Sergey Senozhatsky
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