netdev - Re: [PATCH 5/5] net: mvneta: replace Tx timer with a real interrupt

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Date:	Tue, 14 Jan 2014 00:22:03 +0100
From:	arno@...isbad.org (Arnaud Ebalard)
To:	Willy Tarreau <w@....eu>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH 5/5] net: mvneta: replace Tx timer with a real interrupt

Hi Willy,

Willy Tarreau <w@....eu> writes:

> @@ -1935,14 +1907,22 @@ static int mvneta_poll(struct napi_struct *napi, int budget)
>  
>  	/* Read cause register */
>  	cause_rx_tx = mvreg_read(pp, MVNETA_INTR_NEW_CAUSE) &
> -		MVNETA_RX_INTR_MASK(rxq_number);
> +		(MVNETA_RX_INTR_MASK(rxq_number) | MVNETA_TX_INTR_MASK(txq_number));
> +
> +	/* Release Tx descriptors */
> +	if (cause_rx_tx & MVNETA_TX_INTR_MASK_ALL) {
> +		int tx_todo = 0;
> +
> +		mvneta_tx_done_gbe(pp, (cause_rx_tx & MVNETA_TX_INTR_MASK_ALL), &tx_todo);
> +		cause_rx_tx &= ~MVNETA_TX_INTR_MASK_ALL;
> +	}

Unless I missed something, tx_todo above is just here to make the
compiler happy w/ current prototype of mvneta_tx_done_gbe() but is
otherwise unused: you could simply remove the third parameter of the
function (it is only used here) and remove tx_todo.

Additionally, as you do not use the return value of the function, you
could probably make it void and spare some additional cycles by removing
the computation of the return value. While at it, mvneta_txq_done()
could also be made void.

The patch below gives the idea, it's compile-tested only and applies on
your whole set (fixes + perf).

Index: linux/drivers/net/ethernet/marvell/mvneta.c
===================================================================
--- linux.orig/drivers/net/ethernet/marvell/mvneta.c	2014-01-14 00:07:18.728729578 +0100
+++ linux/drivers/net/ethernet/marvell/mvneta.c	2014-01-14 00:11:57.740949448 +0100
@@ -1314,25 +1314,23 @@
 }
 
 /* Handle end of transmission */
-static int mvneta_txq_done(struct mvneta_port *pp,
+static void mvneta_txq_done(struct mvneta_port *pp,
 			   struct mvneta_tx_queue *txq)
 {
 	struct netdev_queue *nq = netdev_get_tx_queue(pp->dev, txq->id);
 	int tx_done;
 
 	tx_done = mvneta_txq_sent_desc_proc(pp, txq);
-	if (tx_done == 0)
-		return tx_done;
-	mvneta_txq_bufs_free(pp, txq, tx_done);
+	if (tx_done) {
+		mvneta_txq_bufs_free(pp, txq, tx_done);
 
-	txq->count -= tx_done;
+		txq->count -= tx_done;
 
-	if (netif_tx_queue_stopped(nq)) {
-		if (txq->size - txq->count >= MAX_SKB_FRAGS + 1)
-			netif_tx_wake_queue(nq);
+		if (netif_tx_queue_stopped(nq)) {
+			if (txq->size - txq->count >= MAX_SKB_FRAGS + 1)
+				netif_tx_wake_queue(nq);
+		}
 	}
-
-	return tx_done;
 }
 
 static void *mvneta_frag_alloc(const struct mvneta_port *pp)
@@ -1704,30 +1702,23 @@
 /* Handle tx done - called in softirq context. The <cause_tx_done> argument
  * must be a valid cause according to MVNETA_TXQ_INTR_MASK_ALL.
  */
-static u32 mvneta_tx_done_gbe(struct mvneta_port *pp, u32 cause_tx_done,
-			      int *tx_todo)
+static void mvneta_tx_done_gbe(struct mvneta_port *pp, u32 cause_tx_done)
 {
 	struct mvneta_tx_queue *txq;
-	u32 tx_done = 0;
 	struct netdev_queue *nq;
 
-	*tx_todo = 0;
 	while (cause_tx_done) {
 		txq = mvneta_tx_done_policy(pp, cause_tx_done);
 
 		nq = netdev_get_tx_queue(pp->dev, txq->id);
 		__netif_tx_lock(nq, smp_processor_id());
 
-		if (txq->count) {
-			tx_done += mvneta_txq_done(pp, txq);
-			*tx_todo += txq->count;
-		}
+		if (txq->count)
+			mvneta_txq_done(pp, txq);
 
 		__netif_tx_unlock(nq);
 		cause_tx_done &= ~((1 << txq->id));
 	}
-
-	return tx_done;
 }
 
 /* Compute crc8 of the specified address, using a unique algorithm ,
@@ -1961,9 +1952,7 @@
 
 	/* Release Tx descriptors */
 	if (cause_rx_tx & MVNETA_TX_INTR_MASK_ALL) {
-		int tx_todo = 0;
-
-		mvneta_tx_done_gbe(pp, (cause_rx_tx & MVNETA_TX_INTR_MASK_ALL), &tx_todo);
+		mvneta_tx_done_gbe(pp, (cause_rx_tx & MVNETA_TX_INTR_MASK_ALL));
 		cause_rx_tx &= ~MVNETA_TX_INTR_MASK_ALL;
 	}
 
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