From: Oleg Nesterov <oleg@redhat.com>
To: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.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: Thu, 13 Dec 2012 17:17:09 +0100 [thread overview]
Message-ID: <20121213161709.GA19125@redhat.com> (raw)
In-Reply-To: <50C9F38F.3020005@linux.vnet.ibm.com>
On 12/13, Srivatsa S. Bhat wrote:
>
> On 12/13/2012 12:42 AM, Srivatsa S. Bhat wrote:
> >
> > Even I don't spot anything wrong with it. But I'll give it some more
> > thought..
>
> Since an interrupt handler can also run get_online_cpus_atomic(), we
> cannot use the __this_cpu_* versions for modifying reader_percpu_refcnt,
> right?
Hmm. I thought that __this_cpu_* must be safe under preempt_disable().
IOW, I thought that, say, this_cpu_inc() is "equal" to preempt_disable +
__this_cpu_inc() correctness-wise.
And. I thought that this_cpu_inc() is safe wrt interrupt, like local_t.
But when I try to read the comments percpu.h, I am starting to think that
even this_cpu_inc() is not safe if irq handler can do the same?
Confused...
I am shy to ask... will, say, DEFINE_PER_CPU(local_t) and
local_inc(__this_cpu_ptr(...)) work??
> But still, this scheme is better, because the reader doesn't have to spin
> on the read_lock() with interrupts disabled.
Yes, but my main concern is that irq_disable/enable itself is not that cheap.
Oleg.
next prev parent reply other threads:[~2012-12-13 16:17 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
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 [this message]
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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