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

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Message-ID: <CAOS58YMq1DiWgHGsjpABhaeYs9RjRgkHoifQQUKTKNi876bNgQ@mail.gmail.com>
Date:	Wed, 30 May 2012 15:28:37 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Asias He <asias@...hat.com>
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

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.

-- 
tejun
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