On 2019-01-22 1:25 p.m., Bart Van Assche wrote:
The default behavior of the SCSI core is to set the block layer request
queue parameter max_segment_size to 64 KB. That means that elements of
scatterlists are limited to 64 KB. Since RDMA adapters support larger
sizes, increase max_segment_size for the SRP initiator.
Notes:
- The SCSI max_segment_size parameter was introduced in kernel v5.0. See
also commit 50c2e9107f17 ("scsi: introduce a max_segment_size
host_template parameters").
- Some other block drivers already set max_segment_size to UINT_MAX,
e.g. nbd and rbd.
In my sg v4 driver rewrite one of options within the SG_SET_GET_EXTENDED
ioctl is to allow the user to modify this value. It is a #define to
32 KB in the production sg v3 driver.
Doug Gilbert
Cc: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
drivers/infiniband/ulp/srp/ib_srp.c | 1 +
include/rdma/ib_verbs.h | 13 +++++++++++++
2 files changed, 14 insertions(+)
diff --git a/drivers/infiniband/ulp/srp/ib_srp.c b/drivers/infiniband/ulp/srp/ib_srp.c
index 085dba075651..a1173e0992e6 100644
--- a/drivers/infiniband/ulp/srp/ib_srp.c
+++ b/drivers/infiniband/ulp/srp/ib_srp.c
@@ -3819,6 +3819,7 @@ static ssize_t srp_create_target(struct device *dev,
target_host->max_id = 1;
target_host->max_lun = -1LL;
target_host->max_cmd_len = sizeof ((struct srp_cmd *) (void *) 0L)->cdb;
+ target_host->max_segment_size = ib_dma_max_seg_size(ibdev);
target = host_to_target(target_host);
diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 94b6e1dd4dab..71ea144ec823 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -3715,6 +3715,19 @@ static inline unsigned int ib_sg_dma_len(struct ib_device *dev,
return sg_dma_len(sg);
}
+/**
+ * ib_dma_max_seg_size - Return the size limit of a single DMA transfer
+ * @dev: The device to query
+ *
+ * The returned value represents a size in bytes.
+ */
+static inline unsigned int ib_dma_max_seg_size(struct ib_device *dev)
+{
+ struct device_dma_parameters *p = dev->dma_device->dma_parms;
+
+ return p ? p->max_segment_size : UINT_MAX;
+}
+
/**
* ib_dma_sync_single_for_cpu - Prepare DMA region to be accessed by CPU
* @dev: The device for which the DMA address was created
