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

[Jens Axboe]

On 03/12/2014 11:18 AM, David Vrabel wrote:
> On 12/03/14 17:08, Felipe Franciosi wrote:
> > On Wed, Mar 12, 2014 at 4:16 PM, Jens Axboe <axboe@xxxxxxxxx> 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.

That's because most other drivers hook in the appropriate place, and the 
blk_queue_bounce() is then done by the block layer.

--
Jens Axboe

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