linux-kernel - Re: [PATCH] USB: f_mass_storage: dynamic buffers for better alignment

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Date:	Mon, 15 Mar 2010 20:10:21 +0200
From:	Felipe Balbi <me@...ipebalbi.com>
To:	Michal Nazarewicz <m.nazarewicz@...sung.com>
Cc:	linux-usb@...r.kernel.org,
	David Brownell <dbrownell@...rs.sourceforge.net>,
	gregkh@...e.de, linux-kernel@...r.kernel.org,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH] USB: f_mass_storage: dynamic buffers for better
 alignment

On Mon, Mar 15, 2010 at 11:09:55AM +0100, Michal Nazarewicz wrote:
> "Static" buffers in fsg_buffhd structure (ie. fields which are arrays
> rather then pointers to dynamically allocated memory) are not aligned
> to any "big" power of two which may lead to poor DMA performance

not so true as you can add __attribute__ ((aligned(32))) to those.

> @@ -2747,13 +2746,18 @@ static struct fsg_common *fsg_common_init(struct fsg_common *common,
>  
>  
>  	/* Data buffers cyclic list */
> -	/* Buffers in buffhds are static -- no need for additional
> -	 * allocation. */
>  	bh = common->buffhds;
> -	i = FSG_NUM_BUFFERS - 1;
> -	do {
> +	i = FSG_NUM_BUFFERS;
> +	for (i = FSG_NUM_BUFFERS;; ++bh) {

something like

for (i = 0; i < FSG_NUM_BUFFERS; i++, ++bh) {

wouldn't it do it ??

-- 
balbi
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