From: David Woodhouse <david.woodho...@intel.com> This is a minor optimisation, but as a side-effect it means we can know precisely which descriptors were already in the ring when we last prodded it to run.
This will give us a better chance to catch the case where we get a
TxEmpty interrupt when it hasn't actually finished the descriptors we
*know* it should have seen, before it ends up being a full-blown TX
timeout and reset.
Since QEMU's emulation doesn't give TxEmpty interrupts, *always* bash on
TxPoll until we see the first TxEmpty interrupt and cp->txempty_seen
gets set.
Signed-off-by: David Woodhouse <david.woodho...@intel.com>
---
I'm actually having second thoughts about this one since realising that
QEMU doesn't implement it correctly. The workaround isn't *that* horrid
but it's not clear it's enough of a performance win — or whether it's
entirely necessary for catching my TX stall.
drivers/net/ethernet/realtek/8139cp.c | 37 +++++++++++++++++++++++++++++------
1 file changed, 31 insertions(+), 6 deletions(-)
diff --git a/drivers/net/ethernet/realtek/8139cp.c
b/drivers/net/ethernet/realtek/8139cp.c
index 6feff9f..67a4fcf 100644
--- a/drivers/net/ethernet/realtek/8139cp.c
+++ b/drivers/net/ethernet/realtek/8139cp.c
@@ -340,6 +340,9 @@ struct cp_private {
unsigned tx_head ____cacheline_aligned;
unsigned tx_tail;
+ unsigned tx_running;
+ unsigned txempty_seen;
+
struct cp_desc *tx_ring;
struct sk_buff *tx_skb[CP_TX_RING_SIZE];
u32 tx_opts[CP_TX_RING_SIZE];
@@ -611,6 +614,22 @@ static irqreturn_t cp_interrupt (int irq, void
*dev_instance)
if (status & (TxOK | TxErr | TxEmpty | SWInt))
handled |= cp_tx(cp);
+ if ((status & TxEmpty) && cp->tx_running) {
+ handled = 1;
+ /* Qemu's emulation doesn't give TxEmpty interrupts */
+ cp->txempty_seen = 1;
+ if (cp->tx_head == cp->tx_tail) {
+ /* Out of descriptors and we have nothing more for it.
+ Let it stop. */
+ cp->tx_running = 0;
+ } else {
+ /* The hardware raced with us adding a new descriptor,
+ and we didn't get the TxEmpty IRQ in time so we
+ didn't prod it. Prod it now to restart. */
+ cpw8(TxPoll, NormalTxPoll);
+ }
+ }
+
if (status & LinkChg) {
handled = 1;
mii_check_media(&cp->mii_if, netif_msg_link(cp), false);
@@ -796,8 +815,9 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
cp->tx_skb[entry] = skb;
cp->tx_opts[entry] = flags;
- netif_dbg(cp, tx_queued, cp->dev, "tx queued, slot %d, skblen
%d\n",
- entry, skb->len);
+ netif_dbg(cp, tx_queued, cp->dev,
+ "tx queued, slot %d, skblen %d r %d\n",
+ entry, skb->len, cp->tx_running);
} else {
struct cp_desc *txd;
u32 first_len, first_eor, ctrl;
@@ -886,8 +906,9 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
wmb();
cp->tx_opts[first_entry] = ctrl;
- netif_dbg(cp, tx_queued, cp->dev, "tx queued, slots %d-%d,
skblen %d\n",
- first_entry, entry, skb->len);
+ netif_dbg(cp, tx_queued, cp->dev,
+ "tx queued, slots %d-%d, skblen %d r %d\n",
+ first_entry, entry, skb->len, cp->tx_running);
}
cp->tx_head = NEXT_TX(entry);
@@ -895,11 +916,13 @@ static netdev_tx_t cp_start_xmit (struct sk_buff *skb,
if (TX_BUFFS_AVAIL(cp) <= (MAX_SKB_FRAGS + 1))
netif_stop_queue(dev);
+ if (!cp->tx_running || !cp->txempty_seen) {
+ cpw8(TxPoll, NormalTxPoll);
+ cp->tx_running = 1;
+ }
out_unlock:
spin_unlock_irqrestore(&cp->lock, intr_flags);
- cpw8(TxPoll, NormalTxPoll);
-
return NETDEV_TX_OK;
out_dma_error:
dev_kfree_skb_any(skb);
@@ -989,6 +1012,7 @@ static void cp_stop_hw (struct cp_private *cp)
cp->rx_tail = 0;
cp->tx_head = cp->tx_tail = 0;
+ cp->tx_running = 0;
netdev_reset_queue(cp->dev);
}
@@ -1041,6 +1065,7 @@ static inline void cp_start_hw (struct cp_private *cp)
* This variant appears to work fine.
*/
cpw8(Cmd, RxOn | TxOn);
+ cp->tx_running = 0;
netdev_reset_queue(cp->dev);
}
--
2.4.3
--
David Woodhouse Open Source Technology Centre
david.woodho...@intel.com Intel Corporation
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