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

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Message-ID: <532096E8.1010706@citrix.com>
Date:	Wed, 12 Mar 2014 17:18:32 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Felipe Franciosi <felipe@...adoxo.org>
CC:	Jens Axboe <axboe@...nel.dk>, <linux-kernel@...r.kernel.org>,
	Sam Bradshaw <sbradshaw@...ron.com>
Subject: Re: [PATCH 1/2] mtip32xx: Don't bounce IO requests

On 12/03/14 17:08, Felipe Franciosi wrote:
> 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.
[...]
>>> --- 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.
> 
> Hmm... I see what you are saying. David, would you like to comment?

Yes, it should also call blk_queue_bounce_limit(..., BLK_BOUNCE_ANY) in
mtip_block_initialize() as well.

But, only one other driver calls blk_queue_bounce() so it's difficult to
see why this driver would need a call here.

David
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