net/sfc: improve Rx free threshold default

Rx refill in one bulk (which is just 8 descriptors) by default is too
aggressive and makes too many MMIO writes (Rx doorbells) if packet rate
is high. Setting default to 1/8 of Rx descriptors number shows good
performance results. Anyway it is a default value which may be
overridden by Rx configuration provided by application.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>

diff --git a/drivers/net/sfc/sfc_rx.c b/drivers/net/sfc/sfc_rx.c
index 4b1d01e..5d8c276 100644 (file)
--- a/drivers/net/sfc/sfc_rx.c
+++ b/drivers/net/sfc/sfc_rx.c
@@ -974,6 +974,7 @@ sfc_rx_qinit(struct sfc_adapter *sa, unsigned int sw_index,
        struct sfc_rxq *rxq;
        struct sfc_dp_rx_qcreate_info info;
        struct sfc_dp_rx_hw_limits hw_limits;
+       uint16_t rx_free_thresh;
 
        memset(&hw_limits, 0, sizeof(hw_limits));
        hw_limits.rxq_max_entries = sa->rxq_max_entries;
@@ -1043,8 +1044,22 @@ sfc_rx_qinit(struct sfc_adapter *sa, unsigned int sw_index,
        rxq = &sa->rxq_ctrl[sw_index];
        rxq->evq = evq;
        rxq->hw_index = sw_index;
+       /*
+        * If Rx refill threshold is specified (its value is non zero) in
+        * Rx configuration, use specified value. Otherwise use 1/8 of
+        * the Rx descriptors number as the default. It allows to keep
+        * Rx ring full-enough and does not refill too aggressive if
+        * packet rate is high.
+        *
+        * Since PMD refills in bulks waiting for full bulk may be
+        * refilled (basically round down), it is better to round up
+        * here to mitigate it a bit.
+        */
+       rx_free_thresh = (rx_conf->rx_free_thresh != 0) ?
+               rx_conf->rx_free_thresh : EFX_DIV_ROUND_UP(nb_rx_desc, 8);
+       /* Rx refill threshold cannot be smaller than refill bulk */
        rxq_info->refill_threshold =
-               RTE_MAX(rx_conf->rx_free_thresh, SFC_RX_REFILL_BULK);
+               RTE_MAX(rx_free_thresh, SFC_RX_REFILL_BULK);
        rxq_info->refill_mb_pool = mb_pool;
        rxq->buf_size = buf_size;