From: Mikulas Patocka <mpatocka@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ananth N Mavinakayanahalli <ananth@in.ibm.com>,
Anton Arapov <anton@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] percpu-rw-semaphores: use light/heavy barriers
Date: Tue, 23 Oct 2012 17:39:43 -0400 (EDT) [thread overview]
Message-ID: <Pine.LNX.4.64.1210231730270.2689@file.rdu.redhat.com> (raw)
In-Reply-To: <20121023203254.GA3410@linux.vnet.ibm.com>
On Tue, 23 Oct 2012, Paul E. McKenney wrote:
> On Tue, Oct 23, 2012 at 01:29:02PM -0700, Paul E. McKenney wrote:
> > On Tue, Oct 23, 2012 at 08:41:23PM +0200, Oleg Nesterov wrote:
> > > On 10/23, Paul E. McKenney wrote:
> > > >
> > > > * Note that this guarantee implies a further memory-ordering guarantee.
> > > > * On systems with more than one CPU, when synchronize_sched() returns,
> > > > * each CPU is guaranteed to have executed a full memory barrier since
> > > > * the end of its last RCU read-side critical section
> > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> > >
> > > Ah wait... I misread this comment.
> >
> > And I miswrote it. It should say "since the end of its last RCU-sched
> > read-side critical section." So, for example, RCU-sched need not force
> > a CPU that is idle, offline, or (eventually) executing in user mode to
> > execute a memory barrier. Fixed this.
Or you can write "each CPU that is executing a kernel code is guaranteed
to have executed a full memory barrier".
It would be consistent with the current implementation and it would make
it possible to use
barrier()-synchronize_sched() as biased memory barriers.
---
In percpu-rwlocks, CPU 1 executes
...make some writes in the critical section...
barrier();
this_cpu_dec(*p->counters);
and the CPU 2 executes
while (__percpu_count(p->counters))
msleep(1);
synchronize_sched();
So, when CPU 2 finishes synchronize_sched(), we must make sure that
all writes done by CPU 1 are visible to CPU 2.
The current implementation fulfills this requirement, you can just add it
to the specification so that whoever changes the implementation keeps it.
Mikulas
> And I should hasten to add that for synchronize_sched(), disabling
> preemption (including disabling irqs, further including NMI handlers)
> acts as an RCU-sched read-side critical section. (This is in the
> comment header for synchronize_sched() up above my addition to it.)
>
> Thanx, Paul
next prev parent reply other threads:[~2012-10-23 21:40 UTC|newest]
Thread overview: 103+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-15 19:09 [RFC PATCH 0/2] uprobes: register/unregister can race with fork Oleg Nesterov
2012-10-15 19:10 ` [PATCH 1/2] brw_mutex: big read-write mutex Oleg Nesterov
2012-10-15 23:28 ` Paul E. McKenney
2012-10-16 15:56 ` Oleg Nesterov
2012-10-16 18:58 ` Paul E. McKenney
2012-10-17 16:37 ` Oleg Nesterov
2012-10-17 22:28 ` Paul E. McKenney
2012-10-16 19:56 ` Linus Torvalds
2012-10-17 16:59 ` Oleg Nesterov
2012-10-17 22:44 ` Paul E. McKenney
2012-10-18 16:24 ` Oleg Nesterov
2012-10-18 16:38 ` Paul E. McKenney
2012-10-18 17:57 ` Oleg Nesterov
2012-10-18 19:28 ` Mikulas Patocka
2012-10-19 12:38 ` Peter Zijlstra
2012-10-19 15:32 ` Mikulas Patocka
2012-10-19 17:40 ` Peter Zijlstra
2012-10-19 17:57 ` Oleg Nesterov
2012-10-19 22:54 ` Mikulas Patocka
2012-10-24 3:08 ` Dave Chinner
2012-10-25 14:09 ` Mikulas Patocka
2012-10-25 23:40 ` Dave Chinner
2012-10-26 12:06 ` Oleg Nesterov
2012-10-26 13:22 ` Mikulas Patocka
2012-10-26 14:12 ` Oleg Nesterov
2012-10-26 15:23 ` mark_files_ro && sb_end_write Oleg Nesterov
2012-10-26 16:09 ` [PATCH 1/2] brw_mutex: big read-write mutex Mikulas Patocka
2012-10-19 17:49 ` Oleg Nesterov
2012-10-22 23:09 ` Mikulas Patocka
2012-10-23 15:12 ` Oleg Nesterov
2012-10-19 19:28 ` Paul E. McKenney
2012-10-22 23:36 ` [PATCH 0/2] fix and improvements for percpu-rw-semaphores (was: brw_mutex: big read-write mutex) Mikulas Patocka
2012-10-22 23:37 ` [PATCH 1/2] percpu-rw-semaphores: use light/heavy barriers Mikulas Patocka
2012-10-22 23:39 ` [PATCH 2/2] percpu-rw-semaphores: use rcu_read_lock_sched Mikulas Patocka
2012-10-24 16:16 ` Paul E. McKenney
2012-10-24 17:18 ` Oleg Nesterov
2012-10-24 18:20 ` Paul E. McKenney
2012-10-24 18:43 ` Oleg Nesterov
2012-10-24 19:43 ` Paul E. McKenney
2012-10-25 14:54 ` Mikulas Patocka
2012-10-25 15:07 ` Paul E. McKenney
2012-10-25 16:15 ` Mikulas Patocka
2012-10-23 16:59 ` [PATCH 1/2] percpu-rw-semaphores: use light/heavy barriers Oleg Nesterov
2012-10-23 18:05 ` Paul E. McKenney
2012-10-23 18:27 ` Oleg Nesterov
2012-10-23 18:41 ` Oleg Nesterov
2012-10-23 20:29 ` Paul E. McKenney
2012-10-23 20:32 ` Paul E. McKenney
2012-10-23 21:39 ` Mikulas Patocka [this message]
2012-10-24 16:23 ` Paul E. McKenney
2012-10-24 20:22 ` Mikulas Patocka
2012-10-24 20:36 ` Paul E. McKenney
2012-10-24 20:44 ` Mikulas Patocka
2012-10-24 23:57 ` Paul E. McKenney
2012-10-25 12:39 ` Paul E. McKenney
2012-10-25 13:48 ` Mikulas Patocka
2012-10-23 19:23 ` Oleg Nesterov
2012-10-23 20:45 ` Peter Zijlstra
2012-10-23 20:57 ` Peter Zijlstra
2012-10-24 15:11 ` Oleg Nesterov
2012-10-23 21:26 ` Mikulas Patocka
2012-10-23 20:32 ` Peter Zijlstra
2012-10-30 18:48 ` [PATCH 0/2] fix and improvements for percpu-rw-semaphores (was: brw_mutex: big read-write mutex) Oleg Nesterov
2012-10-31 19:41 ` [PATCH 0/1] percpu_rw_semaphore: reimplement to not block the readers unnecessarily Oleg Nesterov
2012-10-31 19:41 ` [PATCH 1/1] " Oleg Nesterov
2012-11-01 15:10 ` Linus Torvalds
2012-11-01 15:34 ` Oleg Nesterov
2012-11-02 18:06 ` [PATCH v2 0/1] " Oleg Nesterov
2012-11-02 18:06 ` [PATCH v2 1/1] " Oleg Nesterov
2012-11-07 17:04 ` [PATCH v3 " Mikulas Patocka
2012-11-07 17:47 ` Oleg Nesterov
2012-11-07 19:17 ` Mikulas Patocka
2012-11-08 13:42 ` Oleg Nesterov
2012-11-08 1:23 ` Paul E. McKenney
2012-11-08 1:16 ` [PATCH v2 " Paul E. McKenney
2012-11-08 13:33 ` Oleg Nesterov
2012-11-08 16:27 ` Paul E. McKenney
2012-11-08 13:48 ` [PATCH RESEND v2 0/1] " Oleg Nesterov
2012-11-08 13:48 ` [PATCH RESEND v2 1/1] " Oleg Nesterov
2012-11-08 20:07 ` Andrew Morton
2012-11-08 21:08 ` Paul E. McKenney
2012-11-08 23:41 ` Mikulas Patocka
2012-11-09 0:41 ` Paul E. McKenney
2012-11-09 3:23 ` Paul E. McKenney
2012-11-09 16:35 ` Oleg Nesterov
2012-11-09 16:59 ` Paul E. McKenney
2012-11-09 12:47 ` Mikulas Patocka
2012-11-09 15:46 ` Oleg Nesterov
2012-11-09 17:01 ` Paul E. McKenney
2012-11-09 18:10 ` Oleg Nesterov
2012-11-09 18:19 ` Oleg Nesterov
2012-11-10 0:55 ` Paul E. McKenney
2012-11-11 15:45 ` Oleg Nesterov
2012-11-12 18:38 ` Paul E. McKenney
2012-11-11 18:27 ` [PATCH -mm] percpu_rw_semaphore-reimplement-to-not-block-the-readers-unnecessari ly.fix Oleg Nesterov
2012-11-12 18:31 ` Paul E. McKenney
2012-11-16 23:22 ` Andrew Morton
2012-11-18 19:32 ` Oleg Nesterov
2012-11-01 15:43 ` [PATCH 1/1] percpu_rw_semaphore: reimplement to not block the readers unnecessarily Paul E. McKenney
2012-11-01 18:33 ` Oleg Nesterov
2012-11-02 16:18 ` Oleg Nesterov
2012-10-15 19:10 ` [PATCH 2/2] uprobes: Use brw_mutex to fix register/unregister vs dup_mmap() race Oleg Nesterov
2012-10-18 7:03 ` Srikar Dronamraju
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