linux-kernel - Re: [PATCH 2/6] irq_work: Implement remote queueing

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Message-ID: <53AAFF74.8090308@linux.vnet.ibm.com>
Date:	Wed, 25 Jun 2014 22:27:24 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Stephen Warren <swarren@...dotorg.org>
CC:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Kevin Hilman <khilman@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH 2/6] irq_work: Implement remote queueing

On 06/25/2014 10:08 PM, Peter Zijlstra wrote:
> On Wed, Jun 25, 2014 at 10:23:21AM -0600, Stephen Warren wrote:
>> On 06/25/2014 04:19 AM, Peter Zijlstra wrote:
>>> On Wed, Jun 25, 2014 at 03:24:11PM +0530, Srivatsa S. Bhat wrote:
>>>> Wait, that was a stupid idea. hotplug_cfd() already invokes irq_work_run
>>>> indirectly via flush_smp_call_function_queue(). So irq_work_cpu_notify()
>>>> doesn't need to invoke it again, AFAIU. So perhaps we can get rid of
>>>> irq_work_cpu_notify() altogether?
>>>
>>> Just so...
>>>
>>> getting up at 6am and sitting in an airport terminal doesn't seem to
>>> agree with me; any more silly fail here?
>>>
>>> ---
>>> Subject: irq_work: Remove BUG_ON in irq_work_run()
>>> From: Peter Zijlstra <peterz@...radead.org>
>>> Date: Wed Jun 25 07:13:07 CEST 2014
>>>
>>> Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any
>>> pending IPI callbacks before CPU offline"), which ends up calling
>>> hotplug_cfd()->flush_smp_call_function_queue()->irq_work_run(), which
>>> is not from IRQ context.
>>>
>>> And since that already calls irq_work_run() from the hotplug path,
>>> remove our entire hotplug handling.
>>
>> Tested-by: Stephen Warren <swarren@...dia.com>
>>
>> [with the s/static// already mentioned in this thread, obviously:-)]
> 
> Right; I pushed out a fixed version right before loosing my tubes at the
> airport :-)
> 
> https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/commit/?h=timers/nohz&id=921d8b81281ecdca686369f52165d04fa3505bd7
> 

This version looks good.

Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>

Regards,
Srivatsa S. Bhat


> I've not gotten wu build bot spam on it so it must be good ;-)
> 
> In any case, I'll add your tested-by and update later this evening.
> 

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