linux-kernel - Re: [PATCH V3] block: Mitigate lock unbalance caused by lock switching

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Message-ID: <4FC5C34C.9010005@redhat.com>
Date:	Wed, 30 May 2012 14:50:52 +0800
From:	Asias He <asias@...hat.com>
To:	Tejun Heo <tj@...nel.org>
CC:	Tim Gardner <rtg.canonical@...il.com>,
	Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, tim.gardner@...onical.com
Subject: Re: [PATCH V3] block: Mitigate lock unbalance caused by lock switching

On 05/30/2012 02:28 PM, Tejun Heo wrote:
> Hello,
>
> On Wed, May 30, 2012 at 3:28 PM, Asias He<asias@...hat.com>  wrote:
>>> Isn't the 'if' clause superfluous ? You could just do the assignment,
>>> e.g.,
>>>
>>> +       spin_lock_irq(lock);
>>> +       q->queue_lock =&q->__queue_lock;
>>> +       spin_unlock_irq(lock);
>>
>>
>> Well, this saves a if clause but adds an unnecessary assignment if the lock
>> is already internal lock.
>
> It's not hot path. Dirtying the cacheline there doesn't mean anything.
> I don't really care either way but making optimization argument is
> pretty silly here.

I don't care this neither ;-)

-- 
Asias
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