linux-kernel - Re: [PATCH] connector: improved unaligned access error fix

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Date:	Thu, 14 Nov 2013 16:22:32 -0500
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Pete Zaitcev <zaitcev@...hat.com>
CC:	Evgeniy Polyakov <zbr@...emap.net>, Erik Jacobson <erikj@....com>,
	Andrew Morton <akpm@...l.org>,
	Matt Helsley <matthltc@...ibm.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] connector: improved unaligned access error fix

On 11/14/2013 2:45 PM, Pete Zaitcev wrote:
> On Thu, 14 Nov 2013 12:09:21 -0500
> Chris Metcalf <cmetcalf@...era.com> wrote:
>
>> -	__u8 buffer[CN_PROC_MSG_SIZE];
>> +	__u8 buffer[CN_PROC_MSG_SIZE] __aligned(8);
>> -	msg = (struct cn_msg *)buffer;
>> +	msg = buffer_to_cn_msg(buffer);
>>  	ev = (struct proc_event *)msg->data;
>>  	memset(&ev->event_data, 0, sizeof(ev->event_data));
> Why is memset(buffer,0,CN_PROC_MSG_SIZE) not acceptable?

That would be fine from a correctness point of view; I'm happy
either way.  My patch nominally has better performance, for
what that's worth, since the memset() call is for a smaller
range (24 bytes instead of 60).  It also avoids the need for
put_unaligned(), which even on platforms that allow unaligned
stores can still be slower.

I can certainly do a v2 with the larger memset() instead if
that's the consensus.

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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