IB/qib: Optimize pio ack buffer allocation

This patch optimizes pio buffer allocation in the kernel.

For qib, kernel pio buffers are used for sending acks.  The code to
allocate the buffer would always start at 0 until it found a buffer.

This means that an average of 64 comparisions were done on each
allocate, since the busy bit won't be cleared until the bits are
refreshed when buffers are exhausted.

This patch adds two new fields in the devdata struct, last_pio and
min_kernel_pio.  last_pio is the last buffer that was allocated.
min_kernel_pio is the lowest potential available buffer.

min_kernel_pio is modifed as contexts are allocated and deallocted.

Reviewed-by: Ramkrishna Vepa <ramkrishna.vepa@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

1 files changed, 8 insertions, 1 deletions

diff --git a/drivers/infiniband/hw/qib/qib.h b/drivers/infiniband/hw/qib/qib.h
index 6b811e3e8bd..2d638877c4a 100644
--- a/drivers/infiniband/hw/qib/qib.h
+++ b/drivers/infiniband/hw/qib/qib.h
@@ -873,7 +873,14 @@ struct qib_devdata {
          * pio_writing.
          */
         spinlock_t pioavail_lock;
-
+        /*
+         * index of last buffer to optimize search for next
+         */
+        u32 last_pio;
+        /*
+         * min kernel pio buffer to optimize search
+         */
+        u32 min_kernel_pio;
         /*
          * Shadow copies of registers; size indicates read access size.
          * Most of them are readonly, but some are write-only register,