From: "Grant Grundler" <grundler@google.com>
To: "Stefan Richter" <stefanr@s5r6.in-berlin.de>
Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: Scatter-gather segment merges by IOMMU?
Date: Fri, 8 Aug 2008 13:25:59 -0700 [thread overview]
Message-ID: <da824cf30808081325n416ec436y94eebe494d789207@mail.gmail.com> (raw)
In-Reply-To: <489CA21F.1030604@s5r6.in-berlin.de>
On Fri, Aug 8, 2008 at 12:44 PM, Stefan Richter
<stefanr@s5r6.in-berlin.de> wrote:
> Hi all,
>
> the block layer usually tries to merge s/g segments if consecutive segments
> combined fit into the queue's max_segment_size. When such a scatter gather
> list is DMA-mapped, can it happen that an IOMMU collapses the elements even
> further, so that sg_dma_len() of a DMA-mapped s/g segment exceeds
> max_segment_size?
I don't see how. The IOMMU code only collapses the "physical" mappings and
does not add new elements to the SG list. ergo sg_dma_len() shouldn't change.
grant
>
> As I understood some discussions in the past, this could indeed happen,
> which is a nuisance. But I may have misunderstood something, or something
> may have changed in the meantime...
> --
> Stefan Richter
> -=====-==--- =--- -=---
> http://arcgraph.de/sr/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
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>
next prev parent reply other threads:[~2008-08-08 20:26 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-08-08 19:44 Stefan Richter
2008-08-08 20:25 ` Grant Grundler [this message]
2008-08-08 21:21 ` Stefan Richter
2008-08-08 21:31 ` FUJITA Tomonori
2008-08-08 21:58 ` Stefan Richter
2008-08-08 22:17 ` FUJITA Tomonori
2008-08-09 18:20 ` [PATCH] ieee1394: sbp2: enforce s/g segment size limit Stefan Richter
2008-08-09 18:21 ` [PATCH] firewire: fw-sbp2: " Stefan Richter
2008-08-11 19:52 ` Grant Grundler
2008-08-13 9:38 ` Stefan Richter
2008-08-12 17:04 ` [PATCH] ieee1394: sbp2: " Grant Grundler
2008-08-12 23:44 ` FUJITA Tomonori
2008-08-13 10:19 ` [PATCH update] " Stefan Richter
2008-08-13 10:20 ` [PATCH update] firewire: fw-sbp2: " Stefan Richter
2008-08-13 10:27 ` [PATCH update] ieee1394: sbp2: " Stefan Richter
2008-08-14 0:55 ` FUJITA Tomonori
2008-08-14 7:12 ` Stefan Richter
2008-08-14 7:21 ` FUJITA Tomonori
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