James.Bottomley@xxxxxxxxxxxxxxxxxxxxx wrote on Tue, 12 Feb 2008 15:10 -0600:
> On Tue, 2008-02-12 at 15:54 -0500, Pete Wyckoff wrote:
> > iscsi_iser does not have any hardware DMA restrictions. Add a
> > slave_configure function to remove any DMA alignment restriction,
> > allowing the use of direct IO from arbitrary offsets within a page.
> > Also disable page bouncing; iser has no restrictions on which pages it
> > can address.
> >
> > Signed-off-by: Pete Wyckoff <pw@xxxxxxx>
> > ---
> > drivers/infiniband/ulp/iser/iscsi_iser.c | 8 ++++++++
> > 1 files changed, 8 insertions(+), 0 deletions(-)
> >
> > diff --git a/drivers/infiniband/ulp/iser/iscsi_iser.c b/drivers/infiniband/ulp/iser/iscsi_iser.c
> > index be1b9fb..1b272a6 100644
> > --- a/drivers/infiniband/ulp/iser/iscsi_iser.c
> > +++ b/drivers/infiniband/ulp/iser/iscsi_iser.c
> > @@ -543,6 +543,13 @@ iscsi_iser_ep_disconnect(__u64 ep_handle)
> > iser_conn_terminate(ib_conn);
> > }
> >
> > +static int iscsi_iser_slave_configure(struct scsi_device *sdev)
> > +{
> > + blk_queue_bounce_limit(sdev->request_queue, BLK_BOUNCE_ANY);
>
> You really don't want to do this. That signals to the block layer that
> we have an iommu, although it's practically the same thing as a 64 bit
> DMA mask ... but I'd just leave it to the DMA mask to set this up
> correctly. Anything else is asking for a subtle bug to turn up years
> from now when something causes the mask and the limit to be mismatched.
Oh. I decided to add that line for symmetry with TCP, and was
convinced by the arguments here:
commit b6d44fe9582b9d90a0b16f508ac08a90d899bf56
Author: Mike Christie <michaelc@xxxxxxxxxxx>
Date: Thu Jul 26 12:46:47 2007 -0500
[SCSI] iscsi_tcp: Turn off bounce buffers
It was found by LSI that on setups with large amounts of memory
we were bouncing buffers when we did not need to. If the iscsi tcp
code touches the data buffer (or a helper does),
it will kmap the buffer. iscsi_tcp also does not interact with hardware,
so it does not have any hw dma restrictions. This patch sets the bounce
buffer settings for our device queue so buffers should not be bounced
because of a driver limit.
I don't see a convenient place to callback into particular iscsi
devices to set the DMA mask per-host. It has to go on the
shost_gendev, right?, but only for TCP and iSER, not qla4xxx, which
handles its DMA mask during device probe.
-- Pete
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