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 v2 01/10] CPU hotplug: Provide APIs for "light" atomic readers to prevent CPU offline
Date: Wed, 5 Dec 2012 20:07:03 +0100 [thread overview]
Message-ID: <20121205190703.GA13795@redhat.com> (raw)
In-Reply-To: <20121205184258.3750.31879.stgit@srivatsabhat.in.ibm.com>
I'll try to read this series later,
one minor and almost offtopic nit.
On 12/06, Srivatsa S. Bhat wrote:
>
> static int __ref take_cpu_down(void *_param)
> {
> struct take_cpu_down_param *param = _param;
> + unsigned long flags;
> int err;
>
> + /*
> + * __cpu_disable() is the step where the CPU is removed from the
> + * cpu_online_mask. Protect it with the light-lock held for write.
> + */
> + write_lock_irqsave(&light_hotplug_rwlock, flags);
> +
> /* Ensure this CPU doesn't handle any more interrupts. */
> err = __cpu_disable();
> - if (err < 0)
> + if (err < 0) {
> + write_unlock_irqrestore(&light_hotplug_rwlock, flags);
> return err;
> + }
> +
> + /*
> + * We have successfully removed the CPU from the cpu_online_mask.
> + * So release the light-lock, so that the light-weight atomic readers
> + * (who care only about the cpu_online_mask updates, and not really
> + * about the actual cpu-take-down operation) can continue.
> + *
> + * But don't enable interrupts yet, because we still have work left to
> + * do, to actually bring the CPU down.
> + */
> + write_unlock(&light_hotplug_rwlock);
>
> cpu_notify(CPU_DYING | param->mod, param->hcpu);
> +
> + local_irq_restore(flags);
> return 0;
This is subjective, but imho _irqsave and the fat comment look confusing.
Currently take_cpu_down() is always called with irqs disabled, so you
do not need to play with interrupts.
10/10 does s/__stop_machine/stop_cpus/ and that patch could simply add
local_irq_disable/enable into take_cpu_down().
But again this is minor and subjective, I won't insist.
Oleg.
next prev parent reply other threads:[~2012-12-05 19:07 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-05 18:42 [RFC PATCH v2 00/10][RESEND] CPU hotplug: stop_machine()-free CPU hotplug Srivatsa S. Bhat
2012-12-05 18:43 ` [RFC PATCH v2 01/10] CPU hotplug: Provide APIs for "light" atomic readers to prevent CPU offline Srivatsa S. Bhat
2012-12-05 18:47 ` Srivatsa S. Bhat
2012-12-05 18:51 ` Srivatsa S. Bhat
2012-12-05 18:53 ` Srivatsa S. Bhat
2012-12-05 18:56 ` Srivatsa S. Bhat
2012-12-05 18:59 ` Srivatsa S. Bhat
2012-12-05 20:14 ` Srivatsa S. Bhat
2012-12-06 16:18 ` Oleg Nesterov
2012-12-06 18:48 ` Srivatsa S. Bhat
2012-12-06 19:17 ` Srivatsa S. Bhat
2012-12-07 21:01 ` Oleg Nesterov
2012-12-06 19:28 ` Steven Rostedt
2012-12-06 19:36 ` Srivatsa S. Bhat
2012-12-06 22:02 ` Steven Rostedt
2012-12-07 17:33 ` Srivatsa S. Bhat
[not found] ` <20121207200014.GB13238@redhat.com>
2012-12-10 18:21 ` Oleg Nesterov
2012-12-10 19:07 ` Steven Rostedt
2012-12-07 19:56 ` Oleg Nesterov
2012-12-07 20:25 ` Srivatsa S. Bhat
2012-12-07 20:59 ` Oleg Nesterov
2012-12-05 19:07 ` Oleg Nesterov [this message]
2012-12-05 19:16 ` Srivatsa S. Bhat
2012-12-05 18:43 ` [RFC PATCH v2 02/10] CPU hotplug: Provide APIs for "full" " Srivatsa S. Bhat
2012-12-05 19:01 ` Srivatsa S. Bhat
2012-12-05 20:31 ` Srivatsa S. Bhat
2012-12-05 20:57 ` Tejun Heo
2012-12-06 4:31 ` Srivatsa S. Bhat
2012-12-05 18:43 ` [RFC PATCH v2 03/10] CPU hotplug: Convert preprocessor macros to static inline functions Srivatsa S. Bhat
2012-12-05 18:43 ` [RFC PATCH v2 04/10] smp, cpu hotplug: Fix smp_call_function_*() to prevent CPU offline properly Srivatsa S. Bhat
2012-12-05 18:43 ` [RFC PATCH v2 05/10] smp, cpu hotplug: Fix on_each_cpu_*() " Srivatsa S. Bhat
2012-12-05 18:44 ` [RFC PATCH v2 06/10] sched, cpu hotplug: Use stable online cpus in try_to_wake_up() & select_task_rq() Srivatsa S. Bhat
2012-12-05 18:44 ` [RFC PATCH v2 07/10] kick_process(), cpu-hotplug: Prevent offlining of target CPU properly Srivatsa S. Bhat
2012-12-05 18:44 ` [RFC PATCH v2 08/10] yield_to(), cpu-hotplug: Prevent offlining of other CPUs properly Srivatsa S. Bhat
2012-12-05 18:44 ` [RFC PATCH v2 09/10] kvm, vmx: Add full atomic synchronization with CPU Hotplug Srivatsa S. Bhat
2012-12-05 18:45 ` [RFC PATCH v2 10/10] cpu: No more __stop_machine() in _cpu_down() Srivatsa S. Bhat
2012-12-05 19:08 ` Oleg Nesterov
2012-12-05 19:12 ` Srivatsa S. Bhat
[not found] <20121205131038.17383.55472.stgit@srivatsabhat.in.ibm.com>
[not found] ` <20121205131136.17383.23318.stgit@srivatsabhat.in.ibm.com>
[not found] ` <20121205142316.GI3885@mtj.dyndns.org>
[not found] ` <20121205164640.GA7382@redhat.com>
[not found] ` <20121205165356.GL3885@mtj.dyndns.org>
2012-12-05 18:15 ` [RFC PATCH v2 01/10] CPU hotplug: Provide APIs for "light" atomic readers to prevent CPU offline Oleg Nesterov
2012-12-05 18:27 ` Tejun Heo
2012-12-05 18:32 ` Srivatsa S. Bhat
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