IB/srp: Make HCA completion vector configurable

Several InfiniBand HCAs allow configuring the completion vector per
CQ.  This allows spreading the workload created by IB completion
interrupts over multiple MSI-X vectors and hence over multiple CPU
cores.  In other words, configuring the completion vector properly not
only allows reducing latency on an initiator connected to multiple
SRP targets but also allows improving throughput.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Acked-by: David Dillow <dillowda@ornl.gov>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/Documentation/ABI/stable/sysfs-driver-ib_srp b/Documentation/ABI/stable/sysfs-driver-ib_srp
index 481aae95c7d1..5c53d28f775c 100644
--- a/Documentation/ABI/stable/sysfs-driver-ib_srp
+++ b/Documentation/ABI/stable/sysfs-driver-ib_srp
@@ -54,6 +54,13 @@ Description:	Interface for making ib_srp connect to a new target.
                   ib_srp. Specifying a value that exceeds cmd_sg_entries is
                   only safe with partial memory descriptor list support enabled
                   (allow_ext_sg=1).
+                * comp_vector, a number in the range 0..n-1 specifying the
+                  MSI-X completion vector. Some HCA's allocate multiple (n)
+                  MSI-X vectors per HCA port. If the IRQ affinity masks of
+                  these interrupts have been configured such that each MSI-X
+                  interrupt is handled by a different CPU then the comp_vector
+                  parameter can be used to spread the SRP completion workload
+                  over multiple CPU's.
 
 What:           /sys/class/infiniband_srp/srp-<hca>-<port_number>/ibdev
 Date:           January 2, 2006