linux-kernel - Re: [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to DMA-able

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Message-Id: <20130730.114900.5636932806999400.davem@davemloft.net>
Date:	Tue, 30 Jul 2013 11:49:00 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	joe@...ches.com
Cc:	gregkh@...uxfoundation.org, hayeswang@...ltek.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-usb@...r.kernel.org, nic_swsd@...ltek.com
Subject: Re: [PATCH v3 1/3] net/usb/r815x: replace USB buffer from stack to
 DMA-able

From: Joe Perches <joe@...ches.com>
Date: Tue, 30 Jul 2013 11:41:17 -0700

> On Tue, 2013-07-30 at 11:33 -0700, David Miller wrote:
>> From: Greg KH <gregkh@...uxfoundation.org>
>> Date: Tue, 30 Jul 2013 07:00:59 -0700
>> 
>> > This call is so slow, you can afford to make a call to kmalloc for the
>> > data, as it sure just did for other structures it needed :)
>> 
>> I told him to implement things this way, to avoid calling kmalloc every
>> single register access.
>> 
>> Using kmalloc all the time makes the access fragile, since a badly timed
>> call during high memory pressure can fail.
>> 
>> I'd rather the potential failure happen at one time, probe time.
>> 
>> In any event, Ming Lei has suggested using usbnet_{read,write}_cmd()
>> instead, which sounds like a good solution to this problem.
> 
> Those do per-call allocs too.

Sigh...  Ok I won't fight this any longer then :-)
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