IB: Increase DMA max_segment_size on Mellanox hardware
By default, each device is assumed to be able only handle 64 KB chunks
during DMA. By giving the segment size a larger value, the block layer
will coalesce more S/G entries together for SRP, allowing larger
requests with the same sg_tablesize setting. The block layer is the
only direct user of it, though a few IOMMU drivers reference it as
well for their *_map_sg coalescing code. pci-gart_64 on x86, and a
smattering on on sparc, powerpc, and ia64.
Since other IB protocols could potentially see larger segments with
this, let's check those:
- iSER is fine, because you limit your maximum request size to 512
KB, so we'll never overrun the page vector in struct iser_page_vec
(128 entries currently). It is independent of the DMA segment size,
and handles multi-page segments already.
- IPoIB is fine, as it maps each page individually, and doesn't use
ib_dma_map_sg().
- RDS appears to do the right thing and has no dependencies on DMA
segment size, but I don't claim to have done a complete audit.
- NFSoRDMA and 9p are OK -- they do not use ib_dma_map_sg(), so they
doesn't care about the coalescing.
- Lustre's ko2iblnd does not care about coalescing -- it properly
walks the returned sg list.
This patch ups the value on Mellanox hardware to 1 GB, which matches
reported firmware limits on mlx4.
Signed-off-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/drivers/infiniband/hw/mthca/mthca_main.c b/drivers/infiniband/hw/mthca/mthca_main.c
index 8a40cd53..f24b79b 100644
--- a/drivers/infiniband/hw/mthca/mthca_main.c
+++ b/drivers/infiniband/hw/mthca/mthca_main.c
@@ -1043,6 +1043,9 @@
}
}
+ /* We can handle large RDMA requests, so allow larger segments. */
+ dma_set_max_seg_size(&pdev->dev, 1024 * 1024 * 1024);
+
mdev = (struct mthca_dev *) ib_alloc_device(sizeof *mdev);
if (!mdev) {
dev_err(&pdev->dev, "Device struct alloc failed, "
diff --git a/drivers/net/mlx4/main.c b/drivers/net/mlx4/main.c
index 2765a3c..c835011 100644
--- a/drivers/net/mlx4/main.c
+++ b/drivers/net/mlx4/main.c
@@ -1109,6 +1109,9 @@
}
}
+ /* Allow large DMA segments, up to the firmware limit of 1 GB */
+ dma_set_max_seg_size(&pdev->dev, 1024 * 1024 * 1024);
+
priv = kzalloc(sizeof *priv, GFP_KERNEL);
if (!priv) {
dev_err(&pdev->dev, "Device struct alloc failed, "