igc: Get rid of spurious interrupts

When running the igc with XDP/ZC in busy polling mode with deferral of hard
interrupts, interrupts still happen from time to time. That is caused by
the igc task watchdog which triggers Rx interrupts periodically.

That mechanism has been introduced to overcome skb/memory allocation
failures [1]. So the Rx clean functions stop processing the Rx ring in case
of such failure. The task watchdog triggers Rx interrupts periodically in
the hope that memory became available in the mean time.

The current behavior is undesirable for real time applications, because the
driver induced Rx interrupts trigger also the softirq processing. However,
all real time packets should be processed by the application which uses the
busy polling method.

Therefore, only trigger the Rx interrupts in case of real allocation
failures. Introduce a new flag for signaling that condition.

[1] - https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git/commit/?id=3be507547e6177e5c808544bd6a2efa2c7f1d436

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Kurt Kanzenbach <kurt@linutronix.de>
Reviewed-by: Simon Horman <horms@kernel.org>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index 8642d67af6ccc21be65fe608967709eac06395e5..eac0f966e0e4c5237475c7321f50cae65a395606 100644 (file)
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -687,6 +687,7 @@ enum igc_ring_flags_t {
        IGC_RING_FLAG_TX_DETECT_HANG,
        IGC_RING_FLAG_AF_XDP_ZC,
        IGC_RING_FLAG_TX_HWTSTAMP,
+       IGC_RING_FLAG_RX_ALLOC_FAILED,
 };
 
 #define ring_uses_large_buffer(ring) \

diff --git a/drivers/net/ethernet/intel/igc/igc_main.c b/drivers/net/ethernet/intel/igc/igc_main.c
index 96b2f2a37bc3d78f33a4b450b71d6d3fa335c964..da322899e834cb13dc24ad1d07b6ab12bbfabd1c 100644 (file)
--- a/drivers/net/ethernet/intel/igc/igc_main.c
+++ b/drivers/net/ethernet/intel/igc/igc_main.c
@@ -2191,6 +2191,7 @@ static bool igc_alloc_mapped_page(struct igc_ring *rx_ring,
        page = dev_alloc_pages(igc_rx_pg_order(rx_ring));
        if (unlikely(!page)) {
                rx_ring->rx_stats.alloc_failed++;
+               set_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
                return false;
        }
 
@@ -2207,6 +2208,7 @@ static bool igc_alloc_mapped_page(struct igc_ring *rx_ring,
                __free_page(page);
 
                rx_ring->rx_stats.alloc_failed++;
+               set_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
                return false;
        }
 
@@ -2658,6 +2660,7 @@ static int igc_clean_rx_irq(struct igc_q_vector *q_vector, const int budget)
                if (!skb) {
                        rx_ring->rx_stats.alloc_failed++;
                        rx_buffer->pagecnt_bias++;
+                       set_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
                        break;
                }
 
@@ -2738,6 +2741,7 @@ static void igc_dispatch_skb_zc(struct igc_q_vector *q_vector,
        skb = igc_construct_skb_zc(ring, xdp);
        if (!skb) {
                ring->rx_stats.alloc_failed++;
+               set_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &ring->flags);
                return;
        }
 
@@ -5807,11 +5811,29 @@ no_wait:
        if (adapter->flags & IGC_FLAG_HAS_MSIX) {
                u32 eics = 0;
 
-               for (i = 0; i < adapter->num_q_vectors; i++)
-                       eics |= adapter->q_vector[i]->eims_value;
-               wr32(IGC_EICS, eics);
+               for (i = 0; i < adapter->num_q_vectors; i++) {
+                       struct igc_q_vector *q_vector = adapter->q_vector[i];
+                       struct igc_ring *rx_ring;
+
+                       if (!q_vector->rx.ring)
+                               continue;
+
+                       rx_ring = adapter->rx_ring[q_vector->rx.ring->queue_index];
+
+                       if (test_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags)) {
+                               eics |= q_vector->eims_value;
+                               clear_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
+                       }
+               }
+               if (eics)
+                       wr32(IGC_EICS, eics);
        } else {
-               wr32(IGC_ICS, IGC_ICS_RXDMT0);
+               struct igc_ring *rx_ring = adapter->rx_ring[0];
+
+               if (test_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags)) {
+                       clear_bit(IGC_RING_FLAG_RX_ALLOC_FAILED, &rx_ring->flags);
+                       wr32(IGC_ICS, IGC_ICS_RXDMT0);
+               }
        }
 
        igc_ptp_tx_hang(adapter);