From: Byungchul Park <byungchul.park@lge.com> To: Steven Rostedt <rostedt@goodmis.org> 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>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, yuwang.yuwang@alibabab-inc.com, 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, kernel-team@lge.com Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Date: Mon, 27 Nov 2017 17:48:22 +0900 [thread overview] Message-ID: <20171127084822.GA15859@X58A-UD3R> (raw) In-Reply-To: <20171108102723.602216b1@gandalf.local.home> On Wed, Nov 08, 2017 at 10:27:23AM -0500, Steven Rostedt wrote: > --- linux-trace.git.orig/kernel/printk/printk.c > +++ linux-trace.git/kernel/printk/printk.c > @@ -86,8 +86,15 @@ EXPORT_SYMBOL_GPL(console_drivers); > static struct lockdep_map console_lock_dep_map = { > .name = "console_lock" > }; > +static struct lockdep_map console_owner_dep_map = { > + .name = "console_owner" > +}; > #endif > > +static DEFINE_RAW_SPINLOCK(console_owner_lock); > +static struct task_struct *console_owner; > +static bool console_waiter; > + > enum devkmsg_log_bits { > __DEVKMSG_LOG_BIT_ON = 0, > __DEVKMSG_LOG_BIT_OFF, > @@ -1753,8 +1760,56 @@ asmlinkage int vprintk_emit(int facility > * semaphore. The release will print out buffers and wake up > * /dev/kmsg and syslog() users. > */ > - if (console_trylock()) > + if (console_trylock()) { > console_unlock(); > + } else { > + struct task_struct *owner = NULL; > + bool waiter; > + bool spin = false; > + > + printk_safe_enter_irqsave(flags); > + > + raw_spin_lock(&console_owner_lock); > + owner = READ_ONCE(console_owner); > + waiter = READ_ONCE(console_waiter); > + if (!waiter && owner && owner != current) { > + WRITE_ONCE(console_waiter, true); > + spin = true; > + } > + raw_spin_unlock(&console_owner_lock); > + > + /* > + * If there is an active printk() writing to the > + * consoles, instead of having it write our data too, > + * see if we can offload that load from the active > + * printer, and do some printing ourselves. > + * Go into a spin only if there isn't already a waiter > + * spinning, and there is an active printer, and > + * that active printer isn't us (recursive printk?). > + */ > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); Hello Steven, I think it would be better to use cross-release stuff here, because the waiter waits for an event which happens in another context. > + /* Owner will clear console_waiter on hand off */ > + while (READ_ONCE(console_waiter)) > + cpu_relax(); > + > + 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_); I'm afraid if it's ok even not to lock(or trylock) actually here. Is there any problem if you call console_trylock() instead of mutex_acquire() here? > + 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) { > @@ -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); > + > + /* The waiter may spin on us after setting console_owner */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); If you want to do this speculatively here, I think it would be better to use a read recursive acquisition. I think spin_acquire() is too stong for that purpose - I also mentioned it on workqueue flush code. Don't you think so? > + > 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_); I think this release() can be moved up over 'if (waiter)' because only waiters within the region between acquire() and release() are meaningful. > + > 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_); So this can be removed. Thanks, Byungchul
WARNING: multiple messages have this Message-ID (diff)
From: Byungchul Park <byungchul.park@lge.com> To: Steven Rostedt <rostedt@goodmis.org> 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>, Petr Mladek <pmladek@suse.com>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, yuwang.yuwang@alibabab-inc.com, 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, kernel-team@lge.com Subject: Re: [PATCH v4] printk: Add console owner and waiter logic to load balance console writes Date: Mon, 27 Nov 2017 17:48:22 +0900 [thread overview] Message-ID: <20171127084822.GA15859@X58A-UD3R> (raw) In-Reply-To: <20171108102723.602216b1@gandalf.local.home> On Wed, Nov 08, 2017 at 10:27:23AM -0500, Steven Rostedt wrote: > --- linux-trace.git.orig/kernel/printk/printk.c > +++ linux-trace.git/kernel/printk/printk.c > @@ -86,8 +86,15 @@ EXPORT_SYMBOL_GPL(console_drivers); > static struct lockdep_map console_lock_dep_map = { > .name = "console_lock" > }; > +static struct lockdep_map console_owner_dep_map = { > + .name = "console_owner" > +}; > #endif > > +static DEFINE_RAW_SPINLOCK(console_owner_lock); > +static struct task_struct *console_owner; > +static bool console_waiter; > + > enum devkmsg_log_bits { > __DEVKMSG_LOG_BIT_ON = 0, > __DEVKMSG_LOG_BIT_OFF, > @@ -1753,8 +1760,56 @@ asmlinkage int vprintk_emit(int facility > * semaphore. The release will print out buffers and wake up > * /dev/kmsg and syslog() users. > */ > - if (console_trylock()) > + if (console_trylock()) { > console_unlock(); > + } else { > + struct task_struct *owner = NULL; > + bool waiter; > + bool spin = false; > + > + printk_safe_enter_irqsave(flags); > + > + raw_spin_lock(&console_owner_lock); > + owner = READ_ONCE(console_owner); > + waiter = READ_ONCE(console_waiter); > + if (!waiter && owner && owner != current) { > + WRITE_ONCE(console_waiter, true); > + spin = true; > + } > + raw_spin_unlock(&console_owner_lock); > + > + /* > + * If there is an active printk() writing to the > + * consoles, instead of having it write our data too, > + * see if we can offload that load from the active > + * printer, and do some printing ourselves. > + * Go into a spin only if there isn't already a waiter > + * spinning, and there is an active printer, and > + * that active printer isn't us (recursive printk?). > + */ > + if (spin) { > + /* We spin waiting for the owner to release us */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); Hello Steven, I think it would be better to use cross-release stuff here, because the waiter waits for an event which happens in another context. > + /* Owner will clear console_waiter on hand off */ > + while (READ_ONCE(console_waiter)) > + cpu_relax(); > + > + 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_); I'm afraid if it's ok even not to lock(or trylock) actually here. Is there any problem if you call console_trylock() instead of mutex_acquire() here? > + 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) { > @@ -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); > + > + /* The waiter may spin on us after setting console_owner */ > + spin_acquire(&console_owner_dep_map, 0, 0, _THIS_IP_); If you want to do this speculatively here, I think it would be better to use a read recursive acquisition. I think spin_acquire() is too stong for that purpose - I also mentioned it on workqueue flush code. Don't you think so? > + > 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_); I think this release() can be moved up over 'if (waiter)' because only waiters within the region between acquire() and release() are meaningful. > + > 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_); So this can be removed. Thanks, Byungchul -- 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:[~2017-11-27 8:48 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 [this message] 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 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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