From: Oleg Nesterov <oleg@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
der.herr@hofr.at, Davidlohr Bueso <dave@stgolabs.net>
Subject: Re: [RFC][PATCH 5/5] percpu-rwsem: Optimize readers and reduce global impact
Date: Sat, 30 May 2015 22:49:00 +0200 [thread overview]
Message-ID: <20150530204900.GA17772@redhat.com> (raw)
In-Reply-To: <CA+55aFxVtg7i9Hqg7a4MyQQs8XGH6QUNr06oj87Pf0tG_e1xvQ@mail.gmail.com>
On 05/29, Linus Torvalds wrote:
>
> On Fri, May 29, 2015 at 1:09 PM, Oleg Nesterov <oleg@redhat.com> wrote:
> >
> > Doesn't it need mb() before "state = readers_slow" to ensure
> > "release" semantics?
>
> Please don't do any mb() at all. Just do smp_store_release() if
> release semantics is what you want.
Agreed!
> (And try to make sure to pair it with smp_load_acquire() on the other
> side for things to make sense)
Hmm. I think you are right...
__percpu_down_read() lacks another mb() after the "state != BLOCK"
check for the same reason, and we can use smp_load_acquire(state)
instead.
Oleg.
next prev parent reply other threads:[~2015-05-30 20:49 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-26 11:43 [RFC][PATCH 0/5] Optimize percpu-rwsem Peter Zijlstra
2015-05-26 11:43 ` [RFC][PATCH 1/5] rcu: Create rcu_sync infrastructure Peter Zijlstra
2015-05-30 16:58 ` Paul E. McKenney
2015-05-30 19:16 ` Oleg Nesterov
2015-05-30 19:25 ` Oleg Nesterov
2015-05-31 16:07 ` Paul E. McKenney
2015-05-26 11:43 ` [RFC][PATCH 2/5] rcusync: Introduce struct rcu_sync_ops Peter Zijlstra
2015-05-26 11:43 ` [RFC][PATCH 3/5] rcusync: Add the CONFIG_PROVE_RCU checks Peter Zijlstra
2015-05-26 11:44 ` [RFC][PATCH 4/5] rcusync: Introduce rcu_sync_dtor() Peter Zijlstra
2015-05-26 11:44 ` [RFC][PATCH 5/5] percpu-rwsem: Optimize readers and reduce global impact Peter Zijlstra
2015-05-29 19:45 ` Oleg Nesterov
2015-05-29 20:09 ` Oleg Nesterov
2015-05-29 20:41 ` Linus Torvalds
2015-05-30 20:49 ` Oleg Nesterov [this message]
2015-06-16 11:48 ` Peter Zijlstra
2015-05-30 17:18 ` Paul E. McKenney
2015-05-30 20:04 ` ring_buffer_attach && cond_synchronize_rcu (Was: percpu-rwsem: Optimize readers and reduce global impact) Oleg Nesterov
2015-06-16 11:08 ` Peter Zijlstra
2015-06-16 11:16 ` Peter Zijlstra
2015-06-16 19:03 ` Oleg Nesterov
2015-06-19 17:57 ` [tip:perf/urgent] perf: Fix ring_buffer_attach() RCU sync, again tip-bot for Oleg Nesterov
2015-05-26 18:12 ` [RFC][PATCH 0/5] Optimize percpu-rwsem Linus Torvalds
2015-05-26 18:34 ` Peter Zijlstra
2015-05-26 18:35 ` Tejun Heo
2015-05-26 18:42 ` Davidlohr Bueso
2015-05-26 21:57 ` Linus Torvalds
2015-05-27 9:28 ` Nicholas Mc Guire
2015-06-05 1:45 ` Al Viro
2015-06-05 21:08 ` Oleg Nesterov
2015-06-05 22:11 ` Al Viro
2015-06-05 23:36 ` Oleg Nesterov
2015-05-27 6:53 ` Peter Zijlstra
2015-05-26 18:57 ` Oleg Nesterov
2015-05-26 19:13 ` Oleg Nesterov
2015-05-26 19:29 ` Oleg Nesterov
2015-05-26 19:54 ` Davidlohr Bueso
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