From 7f9e5c48c1078507747434d4c182ab10925bf98a Mon Sep 17 00:00:00 2001 From: David Dillow Date: Mon, 17 Jan 2011 02:09:44 +0000 Subject: 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 Signed-off-by: Roland Dreier --- drivers/infiniband/hw/mthca/mthca_main.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'drivers/infiniband') diff --git a/drivers/infiniband/hw/mthca/mthca_main.c b/drivers/infiniband/hw/mthca/mthca_main.c index 8a40cd539ab..f24b79b805f 100644 --- a/drivers/infiniband/hw/mthca/mthca_main.c +++ b/drivers/infiniband/hw/mthca/mthca_main.c @@ -1043,6 +1043,9 @@ static int __mthca_init_one(struct pci_dev *pdev, int hca_type) } } + /* 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, " -- cgit v1.2.3-70-g09d2