Some devices advertise a large max_fast_reg_page_list_len
capability, but perform optimally when MRs are significantly smaller
than that depth -- probably when the MR itself is no larger than a
page.
By default, the RDMA R/W core API uses max_sge_rd as the maximum
page depth for MRs. For some devices, the value of max_sge_rd is
1, which is also not optimal. Thus, when max_sge_rd is larger than
1, use that value. Otherwise use the value of the
max_fast_reg_page_list_len attribute.
I've tested this with a couple of devices, and it reproducibly
improves the throughput of large I/Os by several percent.
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
net/sunrpc/xprtrdma/frwr_ops.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
index 448e063..49b314d 100644
--- a/net/sunrpc/xprtrdma/frwr_ops.c
+++ b/net/sunrpc/xprtrdma/frwr_ops.c
@@ -191,10 +191,17 @@
if (attrs->device_cap_flags & IB_DEVICE_SG_GAPS_REG)
ia->ri_mrtype = IB_MR_TYPE_SG_GAPS;
- ia->ri_max_frwr_depth =
- min_t(unsigned int, RPCRDMA_MAX_DATA_SEGS,
- attrs->max_fast_reg_page_list_len);
- dprintk("RPC: %s: device's max FR page list len = %u\n",
+ /* Quirk: Some devices advertise a large max_fast_reg_page_list_len
+ * capability, but perform optimally when the MRs are not larger
+ * than a page.
+ */
+ if (attrs->max_sge_rd > 1)
+ ia->ri_max_frwr_depth = attrs->max_sge_rd;
+ else
+ ia->ri_max_frwr_depth = attrs->max_fast_reg_page_list_len;
+ if (ia->ri_max_frwr_depth > RPCRDMA_MAX_DATA_SEGS)
+ ia->ri_max_frwr_depth = RPCRDMA_MAX_DATA_SEGS;
+ dprintk("RPC: %s: max FR page list depth = %u\n",
__func__, ia->ri_max_frwr_depth);
/* Add room for frwr register and invalidate WRs.
