From: Waiman Long <waiman.long@hp.com> To: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Richard Weinberger <richard@nod.at>, Catalin Marinas <catalin.marinas@arm.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Matt Fleming <matt.fleming@intel.com>, Herbert Xu <herbert@gondor.hengli.com.au>, Akinobu Mita <akinobu.mita@gmail.com>, Rusty Russell <rusty@rustcorp.com.au>, Michel Lespinasse <walken@google.com>, Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, "Chandramouleeswaran, Aswin" <aswin@hp.com>, "Norton, Scott J" <scott.norton@hp.com> Subject: Re: [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation Date: Mon, 15 Jul 2013 16:44:32 -0400 [thread overview] Message-ID: <51E45F30.5070707@hp.com> (raw) In-Reply-To: <1373899141.17876.145.camel@gandalf.local.home> On 07/15/2013 10:39 AM, Steven Rostedt wrote: > On Fri, 2013-07-12 at 21:34 -0400, Waiman Long wrote: > >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> >> --- >> >> +/* >> + * The queue read/write lock data structure >> + * The reader stealing flag, if sea,t will enable reader at the head of the > "sea,t"? Should be "if set,". Thank for spotting the typo. It will be fixed in the next version. >> +/** >> + * wait_in_queue - Add to queue and wait until it is at the head >> + * @lock: Pointer to queue read/writer lock structure >> + * @node: Node pointer to be added to the queue >> + */ >> +static __always_inline void >> +wait_in_queue(struct qrwlock *lock, struct qrwnode *node) >> +{ >> + struct qrwnode *prev; >> + >> + node->next = NULL; >> + node->wait = true; >> + barrier(); >> + prev = xchg(&lock->waitq, node); > "barrier()" isn't needed, as xchg() is a full blown smp_mb(), it also > acts as a compiler barrier. Will remove barrier(). >> +/* >> + * queue_read_trylock - try to acquire read lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + * Return: 1 if lock acquired, 0 if failed >> + */ >> +int queue_read_trylock(struct qrwlock *lock) >> +{ >> + struct qrwlock old, new; >> + >> + old.rw = ACCESS_ONCE(lock->rw); >> + if (unlikely(old.writer)) >> + return 0; >> + new.rw = old.rw; >> + new.readers++; >> + >> + if (cmpxchg(&lock->rw, old.rw, new.rw) == old.rw) >> + return 1; >> + cpu_relax(); > What's the cpu_relax() for? It's not in a loop. I put a cpu_relax() after each cacheline contention event. You are right that we don't need a cpu_relax() in the trylock() function here. > >> + return 0; >> +} >> +EXPORT_SYMBOL(queue_read_trylock); >> + >> +/** >> + * queue_write_lock - acquire write lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + */ >> +void queue_write_lock(struct qrwlock *lock) >> +{ >> + struct qrwnode node, *next; >> + >> + if (likely(!ACCESS_ONCE(lock->writer))) { >> + /* >> + * Atomically set the writer to 1, then wait until reader >> + * count goes to 0. >> + */ >> + if (xchg(&lock->writer, 1) == 0) { >> + while (ACCESS_ONCE(lock->readers)) >> + cpu_relax(); >> + return; >> + } >> + cpu_relax(); > Another cpu_relax() outside of a loop. I can remove that one too. >> + >> +/** >> + * queue_write_trylock - try to acquire write lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + * Return: 1 if lock acquired, 0 if failed >> + */ >> +int queue_write_trylock(struct qrwlock *lock) >> +{ >> + struct qrwlock old, new; >> + >> + old.rw = ACCESS_ONCE(lock->rw); >> + if (!old.rw) { >> + /* >> + * Atomically set the writer to 1 if readers = 0 >> + */ >> + new.rw = old.rw; >> + new.writer = 1; >> + if (cmpxchg(&lock->rw, old.rw, new.rw) == old.rw) >> + return 1; >> + cpu_relax(); > Again the cpu_relax with no loop. Ditto. >> + } >> + return 0; >> +} >> +EXPORT_SYMBOL(queue_write_trylock); > I haven't seen anything bad about this with a quick review. But it > should have a more thorough review to check all corner cases. > > -- Steve > Thank for your time. Regards, Longman
WARNING: multiple messages have this Message-ID (diff)
From: Waiman Long <waiman.long@hp.com> To: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>, linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Richard Weinberger <richard@nod.at>, Catalin Marinas <catalin.marinas@arm.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Matt Fleming <matt.fleming@intel.com>, Herbert Xu <herbert@gondor.apana.org.au>, Akinobu Mita <akinobu.mita@gmail.com>, Rusty Russell <rusty@rustcorp.com.au>, Michel Lespinasse <walken@google.com>, Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, "Chandramouleeswaran, Aswin" <aswin@hp.com>, "Norton, Scott J" <scott.norton@hp.com> Subject: Re: [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation Date: Mon, 15 Jul 2013 16:44:32 -0400 [thread overview] Message-ID: <51E45F30.5070707@hp.com> (raw) In-Reply-To: <1373899141.17876.145.camel@gandalf.local.home> On 07/15/2013 10:39 AM, Steven Rostedt wrote: > On Fri, 2013-07-12 at 21:34 -0400, Waiman Long wrote: > >> Signed-off-by: Waiman Long<Waiman.Long@hp.com> >> --- >> >> +/* >> + * The queue read/write lock data structure >> + * The reader stealing flag, if sea,t will enable reader at the head of the > "sea,t"? Should be "if set,". Thank for spotting the typo. It will be fixed in the next version. >> +/** >> + * wait_in_queue - Add to queue and wait until it is at the head >> + * @lock: Pointer to queue read/writer lock structure >> + * @node: Node pointer to be added to the queue >> + */ >> +static __always_inline void >> +wait_in_queue(struct qrwlock *lock, struct qrwnode *node) >> +{ >> + struct qrwnode *prev; >> + >> + node->next = NULL; >> + node->wait = true; >> + barrier(); >> + prev = xchg(&lock->waitq, node); > "barrier()" isn't needed, as xchg() is a full blown smp_mb(), it also > acts as a compiler barrier. Will remove barrier(). >> +/* >> + * queue_read_trylock - try to acquire read lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + * Return: 1 if lock acquired, 0 if failed >> + */ >> +int queue_read_trylock(struct qrwlock *lock) >> +{ >> + struct qrwlock old, new; >> + >> + old.rw = ACCESS_ONCE(lock->rw); >> + if (unlikely(old.writer)) >> + return 0; >> + new.rw = old.rw; >> + new.readers++; >> + >> + if (cmpxchg(&lock->rw, old.rw, new.rw) == old.rw) >> + return 1; >> + cpu_relax(); > What's the cpu_relax() for? It's not in a loop. I put a cpu_relax() after each cacheline contention event. You are right that we don't need a cpu_relax() in the trylock() function here. > >> + return 0; >> +} >> +EXPORT_SYMBOL(queue_read_trylock); >> + >> +/** >> + * queue_write_lock - acquire write lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + */ >> +void queue_write_lock(struct qrwlock *lock) >> +{ >> + struct qrwnode node, *next; >> + >> + if (likely(!ACCESS_ONCE(lock->writer))) { >> + /* >> + * Atomically set the writer to 1, then wait until reader >> + * count goes to 0. >> + */ >> + if (xchg(&lock->writer, 1) == 0) { >> + while (ACCESS_ONCE(lock->readers)) >> + cpu_relax(); >> + return; >> + } >> + cpu_relax(); > Another cpu_relax() outside of a loop. I can remove that one too. >> + >> +/** >> + * queue_write_trylock - try to acquire write lock of a queue read/write lock >> + * @lock : Pointer to queue read/writer lock structure >> + * Return: 1 if lock acquired, 0 if failed >> + */ >> +int queue_write_trylock(struct qrwlock *lock) >> +{ >> + struct qrwlock old, new; >> + >> + old.rw = ACCESS_ONCE(lock->rw); >> + if (!old.rw) { >> + /* >> + * Atomically set the writer to 1 if readers = 0 >> + */ >> + new.rw = old.rw; >> + new.writer = 1; >> + if (cmpxchg(&lock->rw, old.rw, new.rw) == old.rw) >> + return 1; >> + cpu_relax(); > Again the cpu_relax with no loop. Ditto. >> + } >> + return 0; >> +} >> +EXPORT_SYMBOL(queue_write_trylock); > I haven't seen anything bad about this with a quick review. But it > should have a more thorough review to check all corner cases. > > -- Steve > Thank for your time. Regards, Longman
next prev parent reply other threads:[~2013-07-15 20:44 UTC|newest] Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-07-13 1:34 [PATCH RFC 0/2] qrwlock: Introducing a queue read/write lock implementation Waiman Long 2013-07-13 1:34 ` Waiman Long 2013-07-13 1:34 ` [PATCH RFC 1/2] qrwlock: A " Waiman Long 2013-07-13 1:34 ` Waiman Long 2013-07-15 14:39 ` Steven Rostedt 2013-07-15 14:39 ` Steven Rostedt 2013-07-15 20:44 ` Waiman Long [this message] 2013-07-15 20:44 ` Waiman Long 2013-07-15 22:31 ` Thomas Gleixner 2013-07-15 22:31 ` Thomas Gleixner 2013-07-16 1:19 ` Waiman Long 2013-07-16 1:19 ` Waiman Long 2013-07-18 7:42 ` Ingo Molnar 2013-07-18 7:42 ` Ingo Molnar 2013-07-18 7:42 ` Ingo Molnar 2013-07-18 13:40 ` Waiman Long 2013-07-18 13:40 ` Waiman Long 2013-07-18 13:40 ` Waiman Long 2013-07-19 8:40 ` Ingo Molnar 2013-07-19 8:40 ` Ingo Molnar 2013-07-19 8:40 ` Ingo Molnar 2013-07-19 15:30 ` Waiman Long 2013-07-19 15:30 ` Waiman Long 2013-07-19 15:30 ` Waiman Long 2013-07-22 10:34 ` Ingo Molnar 2013-07-22 10:34 ` Ingo Molnar 2013-07-22 10:34 ` Ingo Molnar 2013-07-24 0:03 ` Waiman Long 2013-07-24 0:03 ` Waiman Long 2013-07-24 0:03 ` Waiman Long 2013-07-18 10:22 ` Thomas Gleixner 2013-07-18 10:22 ` Thomas Gleixner 2013-07-18 14:19 ` Waiman Long 2013-07-18 14:19 ` Waiman Long 2013-07-21 5:42 ` Raghavendra K T 2013-07-21 5:42 ` Raghavendra K T 2013-07-21 5:42 ` Raghavendra K T 2013-07-23 23:54 ` Waiman Long 2013-07-23 23:54 ` Waiman Long 2013-07-23 23:54 ` Waiman Long 2013-07-13 1:34 ` [PATCH RFC 2/2] x86 qrwlock: Enable x86 to use queue read/write lock Waiman Long 2013-07-13 1:34 ` Waiman Long 2013-07-18 12:55 [PATCH RFC 1/2] qrwlock: A queue read/write lock implementation George Spelvin 2013-07-18 13:43 ` Waiman Long 2013-07-18 18:46 ` George Spelvin 2013-07-19 15:43 ` Waiman Long 2013-07-19 21:11 ` George Spelvin 2013-07-19 21:35 ` Waiman Long 2013-07-18 13:18 George Spelvin
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