linux-kernel - Re: [PATCH 1/2] mtip32xx: Don't bounce IO requests

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Message-ID: <53208845.5090305@kernel.dk>
Date:	Wed, 12 Mar 2014 10:16:05 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Felipe Franciosi <felipe@...adoxo.org>,
	linux-kernel@...r.kernel.org
CC:	Sam Bradshaw <sbradshaw@...ron.com>
Subject: Re: [PATCH 1/2] mtip32xx: Don't bounce IO requests

On 03/12/2014 10:05 AM, Felipe Franciosi wrote:
> This device support 64-bit DMA and therefore no IO requests needs bouncing.
> On 32-bit systems, blk_queue_bounce() will bounce all IO requests with high
> mem pages. This makes performance really really bad.
>
> Signed-off-by: Felipe Franciosi <felipe@...adoxo.org>
> ---
>   drivers/block/mtip32xx/mtip32xx.c |    2 --
>   1 file changed, 2 deletions(-)
>
> diff --git a/drivers/block/mtip32xx/mtip32xx.c b/drivers/block/mtip32xx/mtip32xx.c
> index 5160269..24c87fdb 100644
> --- a/drivers/block/mtip32xx/mtip32xx.c
> +++ b/drivers/block/mtip32xx/mtip32xx.c
> @@ -4082,8 +4082,6 @@ static void mtip_make_request(struct request_queue *queue, struct bio *bio)
>
>   	sg = mtip_hw_get_scatterlist(dd, &tag, unaligned);
>   	if (likely(sg != NULL)) {
> -		blk_queue_bounce(queue, &bio);
> -
>   		if (unlikely((bio)->bi_vcnt > MTIP_MAX_SG)) {
>   			dev_warn(&dd->pdev->dev,
>   				"Maximum number of SGL entries exceeded\n");

That seems to be because the driver forgets to set the DMA capabilities. 
It needs a blk_queue_bounce_limit() call when it sets up the queue.

-- 
Jens Axboe

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