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

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Date:	Wed, 12 Mar 2014 17:08:19 +0000
From:	Felipe Franciosi <felipe@...adoxo.org>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	linux-kernel@...r.kernel.org, Sam Bradshaw <sbradshaw@...ron.com>,
	david.vrabel@...rix.com
Subject: Re: [PATCH 1/2] mtip32xx: Don't bounce IO requests

On Wed, Mar 12, 2014 at 4:16 PM, Jens Axboe <axboe@...nel.dk> wrote:
>
> 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
>

Hmm... I see what you are saying. David, would you like to comment?

Thanks,
Felipe

p.s. resending as GMail was naughty and sent my previous reply in HTML.
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