sfc: Implement adaptive IRQ moderation

Calculate a score for each 1000 IRQs:
- TX completions are worth 1 point
- RX completions are worth 4 if merged using LRO or 2 otherwise

Reduce moderation if the score is less than 10000, down to a minimum
of 5 us.  Increase moderation if the score is more than 20000, up to
the specified maximum.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 5 deletions

diff --git a/drivers/net/sfc/falcon.c b/drivers/net/sfc/falcon.c
index f42fc60d1df4..23a1b148d5b2 100644
--- a/drivers/net/sfc/falcon.c
+++ b/drivers/net/sfc/falcon.c
@@ -729,6 +729,9 @@ static void falcon_handle_tx_event(struct efx_channel *channel,
                 tx_ev_desc_ptr = EFX_QWORD_FIELD(*event, TX_EV_DESC_PTR);
                 tx_ev_q_label = EFX_QWORD_FIELD(*event, TX_EV_Q_LABEL);
                 tx_queue = &efx->tx_queue[tx_ev_q_label];
+                channel->irq_mod_score +=
+                        (tx_ev_desc_ptr - tx_queue->read_count) &
+                        efx->type->txd_ring_mask;
                 efx_xmit_done(tx_queue, tx_ev_desc_ptr);
         } else if (EFX_QWORD_FIELD(*event, TX_EV_WQ_FF_FULL)) {
                 /* Rewrite the FIFO write pointer */
@@ -898,6 +901,8 @@ static void falcon_handle_rx_event(struct efx_channel *channel,
                         discard = true;
         }
 
+        channel->irq_mod_score += 2;
+
         /* Handle received packet */
         efx_rx_packet(rx_queue, rx_ev_desc_ptr, rx_ev_byte_cnt,
                       checksummed, discard);
@@ -1075,14 +1080,15 @@ void falcon_set_int_moderation(struct efx_channel *channel)
                  * program is based at 0.  So actual interrupt moderation
                  * achieved is ((x + 1) * res).
                  */
-                unsigned int res = 5;
-                channel->irq_moderation -= (channel->irq_moderation % res);
-                if (channel->irq_moderation < res)
-                        channel->irq_moderation = res;
+                channel->irq_moderation -= (channel->irq_moderation %
+                                            FALCON_IRQ_MOD_RESOLUTION);
+                if (channel->irq_moderation < FALCON_IRQ_MOD_RESOLUTION)
+                        channel->irq_moderation = FALCON_IRQ_MOD_RESOLUTION;
                 EFX_POPULATE_DWORD_2(timer_cmd,
                                      TIMER_MODE, TIMER_MODE_INT_HLDOFF,
                                      TIMER_VAL,
-                                     (channel->irq_moderation / res) - 1);
+                                     channel->irq_moderation /
+                                     FALCON_IRQ_MOD_RESOLUTION - 1);
         } else {
                 EFX_POPULATE_DWORD_2(timer_cmd,
                                      TIMER_MODE, TIMER_MODE_DIS,