From: Jan Kara <jack@suse.cz> To: Steven Rostedt <rostedt@goodmis.org> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.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>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, "yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Subject: Re: [PATCH v2] printk: Add console owner and waiter logic to load balance console writes Date: Fri, 3 Nov 2017 11:19:53 +0100 [thread overview] Message-ID: <20171103101953.GA5280@quack2.suse.cz> (raw) In-Reply-To: <20171102130605.05e987e8@gandalf.local.home> Hi, On Thu 02-11-17 13:06:05, Steven Rostedt wrote: > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + /* Owner will clear console_waiter on hand off */ > + while (!READ_ONCE(console_waiter)) > + cpu_relax(); Hum, what prevents us from rescheduling here? And what if the process stored in console_owner is scheduled out? Both seem to be possible with CONFIG_PREEMPT kernel? Unless I'm missing something you will need to disable preemption in some places... Other than that I like the simplicity of your approach. Honza > + > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + > + /* > + * The owner passed the console lock to us. > + * Since we did not spin on console lock, annotate > + * this as a trylock. Otherwise lockdep will > + * complain. > + */ > + mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_); > + console_unlock(); > + printk_safe_enter_irqsave(flags); > + } > + printk_safe_exit_irqrestore(flags); > + > + } > } > > return printed_len; > @@ -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) { > @@ -2215,6 +2271,20 @@ skip: > goto skip; > } > > + /* > + * 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. > + */ > + > + /* The waiter may spin on us after this */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + > + raw_spin_lock(&console_owner_lock); > + console_owner = current; > + raw_spin_unlock(&console_owner_lock); > + > len += msg_print_text(msg, false, text + len, sizeof(text) - len); > if (nr_ext_console_drivers) { > ext_len = msg_print_ext_header(ext_text, > @@ -2232,11 +2302,48 @@ skip: > 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 = 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(); > } > + > + /* > + * If there is an active waiter waiting on the console_lock. > + * Pass off the printing to the waiter, and the waiter > + * will continue printing on its CPU, and when all writing > + * has finished, the last printer will wake up klogd. > + */ > + if (waiter) { > + WRITE_ONCE(console_waiter, false); > + /* The waiter is now free to continue */ > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + /* > + * Hand off console_lock to waiter. The waiter will perform > + * the up(). After this, the waiter is the console_lock owner. > + */ > + mutex_release(&console_lock_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + /* Note, if waiter is set, logbuf_lock is not held */ > + return; > + } > + > console_locked = 0; > > /* Release the exclusive_console once it is used */ -- Jan Kara <jack@suse.com> SUSE Labs, CR
WARNING: multiple messages have this Message-ID (diff)
From: Jan Kara <jack@suse.cz> To: Steven Rostedt <rostedt@goodmis.org> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.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>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, "yuwang.yuwang" <yuwang.yuwang@alibaba-inc.com>, Peter Zijlstra <peterz@infradead.org>, Linus Torvalds <torvalds@linux-foundation.org>, Jan Kara <jack@suse.cz>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Subject: Re: [PATCH v2] printk: Add console owner and waiter logic to load balance console writes Date: Fri, 3 Nov 2017 11:19:53 +0100 [thread overview] Message-ID: <20171103101953.GA5280@quack2.suse.cz> (raw) In-Reply-To: <20171102130605.05e987e8@gandalf.local.home> Hi, On Thu 02-11-17 13:06:05, Steven Rostedt wrote: > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + /* Owner will clear console_waiter on hand off */ > + while (!READ_ONCE(console_waiter)) > + cpu_relax(); Hum, what prevents us from rescheduling here? And what if the process stored in console_owner is scheduled out? Both seem to be possible with CONFIG_PREEMPT kernel? Unless I'm missing something you will need to disable preemption in some places... Other than that I like the simplicity of your approach. Honza > + > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + > + /* > + * The owner passed the console lock to us. > + * Since we did not spin on console lock, annotate > + * this as a trylock. Otherwise lockdep will > + * complain. > + */ > + mutex_acquire(&console_lock_dep_map, 0, 1, _THIS_IP_); > + console_unlock(); > + printk_safe_enter_irqsave(flags); > + } > + printk_safe_exit_irqrestore(flags); > + > + } > } > > return printed_len; > @@ -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) { > @@ -2215,6 +2271,20 @@ skip: > goto skip; > } > > + /* > + * 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. > + */ > + > + /* The waiter may spin on us after this */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); > + > + raw_spin_lock(&console_owner_lock); > + console_owner = current; > + raw_spin_unlock(&console_owner_lock); > + > len += msg_print_text(msg, false, text + len, sizeof(text) - len); > if (nr_ext_console_drivers) { > ext_len = msg_print_ext_header(ext_text, > @@ -2232,11 +2302,48 @@ skip: > 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 = 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(); > } > + > + /* > + * If there is an active waiter waiting on the console_lock. > + * Pass off the printing to the waiter, and the waiter > + * will continue printing on its CPU, and when all writing > + * has finished, the last printer will wake up klogd. > + */ > + if (waiter) { > + WRITE_ONCE(console_waiter, false); > + /* The waiter is now free to continue */ > + spin_release(&console_owner_dep_map, 1, _THIS_IP_); > + /* > + * Hand off console_lock to waiter. The waiter will perform > + * the up(). After this, the waiter is the console_lock owner. > + */ > + mutex_release(&console_lock_dep_map, 1, _THIS_IP_); > + printk_safe_exit_irqrestore(flags); > + /* Note, if waiter is set, logbuf_lock is not held */ > + return; > + } > + > console_locked = 0; > > /* Release the exclusive_console once it is used */ -- Jan Kara <jack@suse.com> SUSE Labs, CR -- 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:[~2017-11-03 10:19 UTC|newest] Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top 2017-10-26 11:28 [PATCH] mm: don't warn about allocations which stall for too long Tetsuo Handa 2017-10-26 11:28 ` Tetsuo Handa 2017-10-26 11:41 ` Michal Hocko 2017-10-26 11:41 ` Michal Hocko 2017-11-08 10:30 ` peter enderborg 2017-11-09 8:52 ` Michal Hocko 2017-11-09 8:52 ` Michal Hocko 2017-11-09 9:34 ` peter enderborg 2017-11-09 10:09 ` Michal Hocko 2017-11-09 10:09 ` Michal Hocko 2017-11-09 10:19 ` Tetsuo Handa 2017-11-09 10:19 ` Tetsuo Handa 2017-10-26 14:37 ` Johannes Weiner 2017-10-26 14:37 ` Johannes Weiner 2017-10-31 19:32 ` Steven Rostedt 2017-11-01 8:30 ` Vlastimil Babka 2017-11-01 8:30 ` Vlastimil Babka 2017-11-01 13:38 ` Petr Mladek 2017-11-01 13:38 ` Petr Mladek 2017-11-01 15:36 ` Steven Rostedt 2017-11-01 15:36 ` Steven Rostedt 2017-11-02 11:46 ` Petr Mladek 2017-11-02 11:46 ` Petr Mladek 2017-11-02 14:49 ` Steven Rostedt 2017-11-02 14:49 ` Steven Rostedt 2017-11-01 15:33 ` Steven Rostedt 2017-11-01 15:33 ` Steven Rostedt 2017-11-01 17:42 ` Vlastimil Babka 2017-11-01 17:42 ` Vlastimil Babka 2017-11-01 17:54 ` Steven Rostedt 2017-11-01 17:54 ` Steven Rostedt 2017-11-02 8:53 ` Sergey Senozhatsky 2017-11-02 8:53 ` Sergey Senozhatsky 2017-11-02 9:14 ` Sergey Senozhatsky 2017-11-02 9:14 ` Sergey Senozhatsky 2017-11-02 14:55 ` Steven Rostedt 2017-11-02 14:55 ` Steven Rostedt 2017-11-02 12:55 ` Michal Hocko 2017-11-02 12:55 ` Michal Hocko 2017-11-02 15:56 ` Steven Rostedt 2017-11-02 15:56 ` Steven Rostedt 2017-11-02 17:06 ` [PATCH v2] printk: Add console owner and waiter logic to load balance console writes Steven Rostedt 2017-11-02 17:06 ` Steven Rostedt 2017-11-02 17:10 ` Steven Rostedt 2017-11-02 17:10 ` Steven Rostedt 2017-11-02 17:38 ` Steven Rostedt 2017-11-02 17:38 ` Steven Rostedt 2017-11-03 10:19 ` Jan Kara [this message] 2017-11-03 10:19 ` Jan Kara 2017-11-03 11:18 ` Steven Rostedt 2017-11-03 11:18 ` Steven Rostedt
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