[dpdk-dev] [PATCH v2 3/5] testpmd: Change rxfreet default to 32

[Bruce Richardson]

To improve performance by using bulk alloc or vectored RX routines, we
need to set rx free threshold (rxfreet) value to 32, so make this the
testpmd default.

Thirty-two is the minimum setting needed to enable either the
bulk alloc or vector RX routines inside the ixgbe driver, so it's
best made the default for that reason. Please see
"check_rx_burst_bulk_alloc_preconditions()" in ixgbe_rxtx.c, and
RX function assignment logic in "ixgbe_dev_rx_queue_setup()" in
the same file.

The difference in IO performance for testpmd when called without any
optional parameters, and using 10G NICs using the ixgbe driver, can be
significant - approx 25% or more.

Updates in V2:
* Updated commit message with additional details

Signed-off-by: Bruce Richardson <bruce.richardson at intel.com>
---
 app/test-pmd/testpmd.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
index 9f6cdc4..f76406f 100644
--- a/app/test-pmd/testpmd.c
+++ b/app/test-pmd/testpmd.c
@@ -225,7 +225,9 @@ struct rte_eth_thresh tx_thresh = {
 /*
  * Configurable value of RX free threshold.
  */
-uint16_t rx_free_thresh = 0; /* Immediately free RX descriptors by default. */
+uint16_t rx_free_thresh = 32; /* Refill RX descriptors once every 32 packets,
+		This setting is needed for ixgbe to enable bulk alloc or vector
+		receive functionality. */
 
 /*
  * Configurable value of RX drop enable.
-- 
1.9.3