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

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Message-ID: <1375209677.2075.129.camel@joe-AO722>
Date:	Tue, 30 Jul 2013 11:41:17 -0700
From:	Joe Perches <joe@...ches.com>
To:	David Miller <davem@...emloft.net>
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

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.


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