linux-kernel - Re: [Patch 3/7] smpboot: Provide infrastructure for percpu hotplug threads

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Date:	Sat, 21 Jul 2012 23:31:16 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>
Subject: Re: [Patch 3/7] smpboot: Provide infrastructure for percpu hotplug
 threads

On 07/21/2012 02:56 PM, Srivatsa S. Bhat wrote:
> On 07/16/2012 04:12 PM, Thomas Gleixner wrote:
>> Provide a generic interface for setting up and tearing down percpu
>> threads.
>>
>> On registration the threads for already online cpus are created and
>> started. On deregistration (modules) the threads are stoppped.
>>
>> During hotplug operations the threads are created, started, parked and
>> unparked. The datastructure for registration provides a pointer to
>> percpu storage space and optional setup, cleanup, park, unpark
>> functions. These functions are called when the thread state changes.
>>
>> Each implementation has to provide a function which is queried and
>> returns whether the thread should run and the thread function itself.
>>
>> The core code handles all state transitions and avoids duplicated code
>> in the call sites.
>>
>> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> 
> Elegant design and very beautiful code!
> It was such a pleasure to read and review it :-)
> 
> Reviewed-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
> 

Of course, the preempt imbalance needs to get resolved, as pointed out
by Paul... Your patchset + his fix worked fine, without throwing any
scheduling-while-atomic splats.

Regards,
Srivatsa S. Bhat

> [ A minor nit below ]
> 
>> ---
>>  include/linux/smpboot.h |   43 +++++++++
>>  kernel/cpu.c            |   10 +-
>>  kernel/smpboot.c        |  229 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  kernel/smpboot.h        |    4 
>>  4 files changed, 285 insertions(+), 1 deletion(-)
>>
>> +
>> +/**
>> + * smpboot_thread_fn - percpu hotplug thread loop function
>> + * @void:	thread data pointer
> 
> s/void/data
> 
>> + *
>> + * Checks for thread stop and park conditions. Calls the necessary
>> + * setup, cleanup, park and unpark functions for the registered
>> + * thread.
>> + *
>> + * Returns 1 when the thread should exit, 0 otherwise.
>> + */
>> +static int smpboot_thread_fn(void *data)
>> +{
>> +	struct smpboot_thread_data *td = data;
>> +	struct smp_hotplug_thread *ht = td->ht;
>> +
> 
> Regards,
> Srivatsa S. Bhat
> 


-- 
Regards,
Srivatsa S. Bhat
IBM Linux Technology Center


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