From: Lai Jiangshan <laijs@cn.fujitsu.com>
To: Oleg Nesterov <oleg@redhat.com>, paulmck@linux.vnet.ibm.com
Cc: Lai Jiangshan <eag0628@gmail.com>,
linux-doc@vger.kernel.org, peterz@infradead.org,
fweisbec@gmail.com, Michel Lespinasse <walken@google.com>,
mingo@kernel.org, linux-arch@vger.kernel.org,
linux@arm.linux.org.uk, xiaoguangrong@linux.vnet.ibm.com,
wangyun@linux.vnet.ibm.com, nikunj@linux.vnet.ibm.com,
linux-pm@vger.kernel.org, rusty@rustcorp.com.au,
rostedt@goodmis.org, rjw@sisk.pl, namhyung@kernel.org,
tglx@linutronix.de, linux-arm-kernel@lists.infradead.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
vincent.guittot@linaro.org, sbw@mit.edu,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
tj@kernel.org, akpm@linux-foundation.org,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH] lglock: add read-preference local-global rwlock
Date: Sat, 02 Mar 2013 21:42:15 +0800 [thread overview]
Message-ID: <513201B7.5070004@cn.fujitsu.com> (raw)
In-Reply-To: <20130301182854.GA3631@redhat.com>
On 02/03/13 02:28, Oleg Nesterov wrote:
> Lai, I didn't read this discussion except the code posted by Michel.
> I'll try to read this patch carefully later, but I'd like to ask
> a couple of questions.
>
> This version looks more complex than Michel's, why? Just curious, I
> am trying to understand what I missed. See
> http://marc.info/?l=linux-kernel&m=136196350213593
Michel changed my old draft version a little, his version is good enough for me.
My new version tries to add a little better nestable support with only
adding single __this_cpu_op() in _read_[un]lock().
>
> And I can't understand FALLBACK_BASE...
>
> OK, suppose that CPU_0 does _write_unlock() and releases ->fallback_rwlock.
>
> CPU_1 does _read_lock(), and ...
>
>> +void lg_rwlock_local_read_lock(struct lgrwlock *lgrw)
>> +{
>> + struct lglock *lg = &lgrw->lglock;
>> +
>> + preempt_disable();
>> + rwlock_acquire_read(&lg->lock_dep_map, 0, 0, _RET_IP_);
>> + if (likely(!__this_cpu_read(*lgrw->reader_refcnt))) {
>> + if (!arch_spin_trylock(this_cpu_ptr(lg->lock))) {
>
> _trylock() fails,
>
>> + read_lock(&lgrw->fallback_rwlock);
>> + __this_cpu_add(*lgrw->reader_refcnt, FALLBACK_BASE);
>
> so we take ->fallback_rwlock and ->reader_refcnt == FALLBACK_BASE.
>
> CPU_0 does lg_global_unlock(lgrw->lglock) and finishes _write_unlock().
>
> Interrupt handler on CPU_1 does _read_lock() notices ->reader_refcnt != 0
> and simply does this_cpu_inc(), so reader_refcnt == FALLBACK_BASE + 1.
>
> Then irq does _read_unlock(), and
>
>> +void lg_rwlock_local_read_unlock(struct lgrwlock *lgrw)
>> +{
>> + switch (__this_cpu_dec_return(*lgrw->reader_refcnt)) {
>> + case 0:
>> + lg_local_unlock(&lgrw->lglock);
>> + return;
>> + case FALLBACK_BASE:
>> + __this_cpu_sub(*lgrw->reader_refcnt, FALLBACK_BASE);
>> + read_unlock(&lgrw->fallback_rwlock);
>
> hits this case?
>
> Doesn't look right, but most probably I missed something.
Your are right, I just realized that I had spit a code which should be atomic.
I hope this patch(V2) can get more reviews.
My first and many locking knowledge is learned from Paul.
Paul, would you also review it?
Thanks,
Lai
>
> Oleg.
>
> --
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next prev parent reply other threads:[~2013-03-02 13:40 UTC|newest]
Thread overview: 115+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-02-18 12:38 [PATCH v6 00/46] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2013-02-18 12:38 ` [PATCH v6 01/46] percpu_rwlock: Introduce the global reader-writer lock backend Srivatsa S. Bhat
2013-02-18 12:38 ` [PATCH v6 02/46] percpu_rwlock: Introduce per-CPU variables for the reader and the writer Srivatsa S. Bhat
2013-02-18 12:38 ` [PATCH v6 03/46] percpu_rwlock: Provide a way to define and init percpu-rwlocks at compile time Srivatsa S. Bhat
2013-02-18 12:38 ` [PATCH v6 04/46] percpu_rwlock: Implement the core design of Per-CPU Reader-Writer Locks Srivatsa S. Bhat
2013-02-18 15:45 ` Michel Lespinasse
2013-02-18 16:21 ` Srivatsa S. Bhat
2013-02-18 16:31 ` Steven Rostedt
2013-02-18 16:46 ` Srivatsa S. Bhat
2013-02-18 17:56 ` Srivatsa S. Bhat
2013-02-18 18:07 ` Michel Lespinasse
2013-02-18 18:14 ` Srivatsa S. Bhat
2013-02-25 15:53 ` Lai Jiangshan
2013-02-25 19:26 ` Srivatsa S. Bhat
2013-02-26 0:17 ` Lai Jiangshan
2013-02-26 0:19 ` Lai Jiangshan
2013-02-26 9:02 ` Srivatsa S. Bhat
2013-02-26 12:59 ` Lai Jiangshan
2013-02-26 14:22 ` Srivatsa S. Bhat
2013-02-26 16:25 ` Lai Jiangshan
2013-02-26 19:30 ` Srivatsa S. Bhat
2013-02-27 0:33 ` Lai Jiangshan
2013-02-27 21:19 ` Srivatsa S. Bhat
2013-03-01 17:44 ` [PATCH] lglock: add read-preference local-global rwlock Lai Jiangshan
2013-03-01 17:53 ` Tejun Heo
2013-03-01 20:06 ` Srivatsa S. Bhat
2013-03-01 18:28 ` Oleg Nesterov
2013-03-02 12:13 ` Michel Lespinasse
2013-03-02 13:14 ` [PATCH V2] " Lai Jiangshan
2013-03-02 17:11 ` Srivatsa S. Bhat
2013-03-05 15:41 ` Lai Jiangshan
2013-03-05 17:55 ` Srivatsa S. Bhat
2013-03-02 17:20 ` Oleg Nesterov
2013-03-03 17:40 ` Oleg Nesterov
2013-03-05 1:37 ` Michel Lespinasse
2013-03-05 15:27 ` Lai Jiangshan
2013-03-05 16:19 ` Michel Lespinasse
2013-03-05 16:41 ` Oleg Nesterov
2013-03-02 17:06 ` [PATCH] " Oleg Nesterov
2013-03-05 15:54 ` Lai Jiangshan
2013-03-05 16:32 ` Michel Lespinasse
2013-03-05 16:35 ` Oleg Nesterov
2013-03-02 13:42 ` Lai Jiangshan [this message]
2013-03-02 17:01 ` Oleg Nesterov
2013-03-01 17:50 ` [PATCH v6 04/46] percpu_rwlock: Implement the core design of Per-CPU Reader-Writer Locks Lai Jiangshan
2013-03-01 19:47 ` Srivatsa S. Bhat
2013-03-05 16:25 ` Lai Jiangshan
2013-03-05 18:27 ` Srivatsa S. Bhat
2013-03-01 18:10 ` Tejun Heo
2013-03-01 19:59 ` Srivatsa S. Bhat
2013-02-27 11:11 ` Michel Lespinasse
2013-02-27 19:25 ` Oleg Nesterov
2013-02-28 11:34 ` Michel Lespinasse
2013-02-28 18:00 ` Oleg Nesterov
2013-02-28 18:20 ` Oleg Nesterov
2013-02-26 13:34 ` Lai Jiangshan
2013-02-26 15:17 ` Srivatsa S. Bhat
2013-02-26 14:17 ` Lai Jiangshan
2013-02-26 14:37 ` Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 05/46] percpu_rwlock: Make percpu-rwlocks IRQ-safe, optimally Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 06/46] percpu_rwlock: Rearrange the read-lock code to fastpath nested percpu readers Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 07/46] percpu_rwlock: Allow writers to be readers, and add lockdep annotations Srivatsa S. Bhat
2013-02-18 15:51 ` Michel Lespinasse
2013-02-18 16:31 ` Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 08/46] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-02-18 16:23 ` Michel Lespinasse
2013-02-18 16:43 ` Srivatsa S. Bhat
2013-02-18 17:21 ` Michel Lespinasse
2013-02-18 18:50 ` Srivatsa S. Bhat
2013-02-19 9:40 ` Michel Lespinasse
2013-02-19 9:55 ` Srivatsa S. Bhat
2013-02-19 10:42 ` David Laight
2013-02-19 10:58 ` Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 09/46] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 10/46] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2013-02-18 12:39 ` [PATCH v6 11/46] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 12/46] sched/timer: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 13/46] sched/migration: Use raw_spin_lock/unlock since interrupts are already disabled Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 14/46] sched/rt: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 15/46] tick: " Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 16/46] time/clocksource: " Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 17/46] clockevents: Use get/put_online_cpus_atomic() in clockevents_notify() Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 18/46] softirq: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-02-18 12:40 ` [PATCH v6 19/46] irq: " Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 20/46] net: " Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 21/46] block: " Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 22/46] crypto: pcrypt - Protect access to cpu_online_mask with get/put_online_cpus() Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 23/46] infiniband: ehca: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 24/46] [SCSI] fcoe: " Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 25/46] staging: octeon: " Srivatsa S. Bhat
2013-02-18 12:41 ` [PATCH v6 26/46] x86: " Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 27/46] perf/x86: " Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 28/46] KVM: Use get/put_online_cpus_atomic() to prevent CPU offline from atomic context Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 29/46] kvm/vmx: Use get/put_online_cpus_atomic() to prevent CPU offline Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 30/46] x86/xen: " Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 31/46] alpha/smp: " Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 32/46] blackfin/smp: " Srivatsa S. Bhat
2013-02-18 12:42 ` [PATCH v6 33/46] cris/smp: " Srivatsa S. Bhat
2013-02-18 13:07 ` Jesper Nilsson
2013-02-18 12:43 ` [PATCH v6 34/46] hexagon/smp: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 35/46] ia64: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 36/46] m32r: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 37/46] MIPS: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 38/46] mn10300: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 39/46] parisc: " Srivatsa S. Bhat
2013-02-18 12:43 ` [PATCH v6 40/46] powerpc: " Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 41/46] sh: " Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 42/46] sparc: " Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 43/46] tile: " Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 44/46] cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 45/46] CPU hotplug, stop_machine: Decouple CPU hotplug from stop_machine() in Kconfig Srivatsa S. Bhat
2013-02-18 12:44 ` [PATCH v6 46/46] Documentation/cpu-hotplug: Remove references to stop_machine() Srivatsa S. Bhat
2013-02-22 0:31 ` [PATCH v6 00/46] CPU hotplug: stop_machine()-free CPU hotplug Rusty Russell
2013-02-25 21:45 ` Srivatsa S. Bhat
2013-03-01 12:05 ` Vincent Guittot
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