From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: tglx@linutronix.de, peterz@infradead.org,
paulmck@linux.vnet.ibm.com, rusty@rustcorp.com.au,
mingo@kernel.org, akpm@linux-foundation.org, namhyung@kernel.org,
vincent.guittot@linaro.org, tj@kernel.org, sbw@mit.edu,
amit.kucheria@linaro.org, rostedt@goodmis.org, rjw@sisk.pl,
wangyun@linux.vnet.ibm.com, xiaoguangrong@linux.vnet.ibm.com,
nikunj@linux.vnet.ibm.com, linux-pm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH v4 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context
Date: Wed, 12 Dec 2012 23:41:21 +0530 [thread overview]
Message-ID: <50C8C8C9.2070605@linux.vnet.ibm.com> (raw)
In-Reply-To: <20121212172431.GA23328@redhat.com>
On 12/12/2012 10:54 PM, Oleg Nesterov wrote:
> On 12/12, Oleg Nesterov wrote:
>>
>> On 12/11, Srivatsa S. Bhat wrote:
>>>
>>> IOW, the hotplug readers just increment/decrement their per-cpu refcounts
>>> when no writer is active.
>>
>> plus cli/sti ;) and increment/decrement are atomic.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> OOPS, sorry I was going to say "adds mb()".
>
Ok, got it :)
> And when I look at get_online_cpus_atomic() again it uses rmb(). This
> doesn't look correct, we need the full barrier between this_cpu_inc()
> and writer_active().
>
Hmm..
> At the same time reader_nested_percpu() can be checked before mb().
>
I thought that since the increment and the check (reader_nested_percpu)
act on the same memory location, they will naturally be run in the given
order, without any need for barriers. Am I wrong?
(I referred Documentation/memory-barriers.txt again to verify this, and
the second point under the "Guarantees" section looked like it said the
same thing : "Overlapping loads and stores within a particular CPU will
appear to be ordered within that CPU").
Regards,
Srivatsa S. Bhat
next prev parent reply other threads:[~2012-12-12 18:13 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-11 14:03 [RFC PATCH v4 0/9] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2012-12-11 14:04 ` [RFC PATCH v4 1/9] CPU hotplug: Provide APIs to prevent CPU offline from atomic context Srivatsa S. Bhat
2012-12-12 17:17 ` Oleg Nesterov
2012-12-12 17:24 ` Oleg Nesterov
2012-12-12 18:11 ` Srivatsa S. Bhat [this message]
2012-12-12 18:23 ` Oleg Nesterov
2012-12-12 18:42 ` Srivatsa S. Bhat
2012-12-12 17:53 ` Srivatsa S. Bhat
2012-12-12 18:02 ` Oleg Nesterov
2012-12-12 18:30 ` Srivatsa S. Bhat
2012-12-12 18:48 ` Oleg Nesterov
2012-12-12 19:12 ` Srivatsa S. Bhat
2012-12-13 15:26 ` Srivatsa S. Bhat
2012-12-13 16:17 ` Oleg Nesterov
2012-12-13 16:32 ` Srivatsa S. Bhat
2012-12-14 18:03 ` Oleg Nesterov
2012-12-18 15:53 ` Srivatsa S. Bhat
2012-12-18 19:43 ` Oleg Nesterov
2012-12-18 20:06 ` Srivatsa S. Bhat
2012-12-19 16:39 ` Oleg Nesterov
2012-12-19 18:16 ` Srivatsa S. Bhat
2012-12-19 19:14 ` Oleg Nesterov
2012-12-19 19:49 ` Srivatsa S. Bhat
2012-12-20 13:42 ` Oleg Nesterov
2012-12-20 14:06 ` Srivatsa S. Bhat
2012-12-22 20:17 ` Srivatsa S. Bhat
2012-12-23 16:42 ` Oleg Nesterov
2012-12-24 15:50 ` Srivatsa S. Bhat
2012-12-13 16:32 ` Tejun Heo
2012-12-12 19:36 ` Oleg Nesterov
2012-12-12 19:43 ` Srivatsa S. Bhat
2012-12-12 21:10 ` Oleg Nesterov
2012-12-11 14:04 ` [RFC PATCH v4 2/9] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2012-12-11 14:04 ` [RFC PATCH v4 3/9] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2012-12-11 14:04 ` [RFC PATCH v4 4/9] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2012-12-11 14:05 ` [RFC PATCH v4 5/9] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() Srivatsa S. Bhat
2012-12-11 14:05 ` [RFC PATCH v4 6/9] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly Srivatsa S. Bhat
2012-12-11 14:05 ` [RFC PATCH v4 7/9] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Srivatsa S. Bhat
2012-12-11 14:05 ` [RFC PATCH v4 8/9] kvm, vmx: Add atomic synchronization with CPU Hotplug Srivatsa S. Bhat
2012-12-11 14:05 ` [RFC PATCH v4 9/9] cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat
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