netdev - [PATCH net v2 5/5] net: stmmac: Prevent RX starvation in stmmac_napi

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Date:   Wed,  9 Jan 2019 10:06:00 +0100
From:   Jose Abreu <jose.abreu@...opsys.com>
To:     netdev@...r.kernel.org
Cc:     Jose Abreu <jose.abreu@...opsys.com>,
        Joao Pinto <joao.pinto@...opsys.com>,
        "David S . Miller" <davem@...emloft.net>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>
Subject: [PATCH net v2 5/5] net: stmmac: Prevent RX starvation in stmmac_napi_poll()

Currently, TX is given a budget which is consumed by stmmac_tx_clean()
and stmmac_rx() is given the remaining non-consumed budget.

This is wrong and in case we are sending a large number of packets this
can starve RX because remaining budget will be low.

Let's give always the same budget for RX and TX clean.

While at it, check if we missed any interrupts while we were in NAPI
callback by looking at DMA interrupt status.

Cc: Joao Pinto <jpinto@...opsys.com>
Cc: David S. Miller <davem@...emloft.net>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: Alexandre Torgue <alexandre.torgue@...com>
Signed-off-by: Jose Abreu <joabreu@...opsys.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 27 ++++++++++++-----------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 83ceb1a12e77..3f23e14891df 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -3525,27 +3525,28 @@ static int stmmac_napi_poll(struct napi_struct *napi, int budget)
 	struct stmmac_channel *ch =
 		container_of(napi, struct stmmac_channel, napi);
 	struct stmmac_priv *priv = ch->priv_data;
-	int work_done = 0, work_rem = budget;
+	int work_done, rx_done = 0, tx_done = 0;
 	u32 chan = ch->index;
 
 	priv->xstats.napi_poll++;
 
-	if (ch->has_tx) {
-		int done = stmmac_tx_clean(priv, work_rem, chan);
+	if (ch->has_tx)
+		tx_done = stmmac_tx_clean(priv, budget, chan);
+	if (ch->has_rx)
+		rx_done = stmmac_rx(priv, budget, chan);
 
-		work_done += done;
-		work_rem -= done;
-	}
-
-	if (ch->has_rx) {
-		int done = stmmac_rx(priv, work_rem, chan);
+	work_done = max(rx_done, tx_done);
+	work_done = min(work_done, budget);
 
-		work_done += done;
-		work_rem -= done;
-	}
+	if (work_done < budget && napi_complete_done(napi, work_done)) {
+		int stat;
 
-	if (work_done < budget && napi_complete_done(napi, work_done))
 		stmmac_enable_dma_irq(priv, priv->ioaddr, chan);
+		stat = stmmac_dma_interrupt_status(priv, priv->ioaddr,
+						   &priv->xstats, chan);
+		if (stat && napi_reschedule(napi))
+			stmmac_disable_dma_irq(priv, priv->ioaddr, chan);
+	}
 
 	return work_done;
 }
-- 
2.7.4