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From: Olivier Matz <olivier.matz@6wind.com>
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Date: Thu, 24 Nov 2016 10:54:20 +0100
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Subject: [dpdk-dev] [RFC 8/9] net/e1000: optimize rx queue descriptor count
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Use a binary search algorithm to find the first empty DD bit. The
ring-empty and ring-full cases are managed separately as they are more
likely to happen.
PR=52423
Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Ivan Boule <ivan.boule@6wind.com>
---
drivers/net/e1000/em_rxtx.c | 55 +++++++++++++++++++++++++++++++++------------
1 file changed, 41 insertions(+), 14 deletions(-)
diff --git a/drivers/net/e1000/em_rxtx.c b/drivers/net/e1000/em_rxtx.c
index c1c724b..a469fd7 100644
--- a/drivers/net/e1000/em_rxtx.c
+++ b/drivers/net/e1000/em_rxtx.c
@@ -1385,24 +1385,51 @@ eth_em_rx_queue_setup(struct rte_eth_dev *dev,
uint32_t
eth_em_rx_queue_count(struct rte_eth_dev *dev, uint16_t rx_queue_id)
{
-#define EM_RXQ_SCAN_INTERVAL 4
- volatile struct e1000_rx_desc *rxdp;
+ volatile uint8_t *status;
struct em_rx_queue *rxq;
- uint32_t desc = 0;
+ uint32_t offset, interval, resolution;
+ int32_t idx;
rxq = dev->data->rx_queues[rx_queue_id];
- rxdp = &(rxq->rx_ring[rxq->rx_tail]);
-
- while ((desc < rxq->nb_rx_desc) &&
- (rxdp->status & E1000_RXD_STAT_DD)) {
- desc += EM_RXQ_SCAN_INTERVAL;
- rxdp += EM_RXQ_SCAN_INTERVAL;
- if (rxq->rx_tail + desc >= rxq->nb_rx_desc)
- rxdp = &(rxq->rx_ring[rxq->rx_tail +
- desc - rxq->nb_rx_desc]);
- }
- return desc;
+ /* check if ring empty */
+ idx = rxq->rx_tail;
+ status = &rxq->rx_ring[idx].status;
+ if (!(*status & E1000_RXD_STAT_DD))
+ return 0;
+
+ /* decrease the precision if ring is large */
+ if (rxq->nb_rx_desc <= 256)
+ resolution = 4;
+ else
+ resolution = 16;
+
+ /* check if ring full */
+ idx = rxq->rx_tail - rxq->nb_rx_hold - resolution;
+ if (idx < 0)
+ idx += rxq->nb_rx_desc;
+ status = &rxq->rx_ring[idx].status;
+ if (*status & E1000_RXD_STAT_DD)
+ return rxq->nb_rx_desc;
+
+ /* use a binary search */
+ interval = (rxq->nb_rx_desc - rxq->nb_rx_hold) >> 1;
+ offset = interval;
+
+ do {
+ idx = rxq->rx_tail + offset;
+ if (idx >= rxq->nb_rx_desc)
+ idx -= rxq->nb_rx_desc;
+
+ interval >>= 1;
+ status = &rxq->rx_ring[idx].status;
+ if (*status & E1000_RXD_STAT_DD)
+ offset += interval;
+ else
+ offset -= interval;
+ } while (interval >= resolution);
+
+ return offset;
}
int
--
2.8.1