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Message-ID: <tkrat.83117f4523f0d928@s5r6.in-berlin.de>
Date: Sat, 13 Nov 2010 23:07:16 +0100 (CET)
From: Stefan Richter <stefanr@...6.in-berlin.de>
To: linux1394-devel@...ts.sourceforge.net
cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: [PATCH update 2] firewire: net: throttle TX queue before running out
of tlabels
This prevents firewire-net from submitting write requests in fast
succession until failure due to all 64 transaction labels were used up
for unfinished split transactions. The netif_stop/wake_queue API is
used for this purpose.
Without this stop/wake mechanism, datagrams were simply lost whenever
the tlabel pool was exhausted. Plus, tlabel exhaustion by firewire-net
also prevented other unrelated outbound transactions to be initiated.
The high watermark is set to considerably less than 64 (I chose 8)
because peers which run current Linux firewire-ohci are still easily
saturated by this (i.e. some datagrams are dropped with ack-busy-*
events), depending on the hardware at transmitter and receiver side.
I did not see changes to resulting throughput that were discernible from
the usual measuring noise. To do: Revisit the choice of queue depth
once firewire-ohci's AR DMA was improved.
I wonder what a good net_device.tx_queue_len value is. I just set it
to the same value as the chosen watermark for now.
Note: This removes some netif_wake_queue from reception code paths.
They were apparently copy&paste artefacts from a nonsensical
netif_wake_queue use in the older eth1394 driver. This belongs only
into the transmit path.
Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
---
Update 2: Maxim told me to de-obfuscate status tracking. I realized
that netif_queue_stopped can be used for that and thereby noticed bogus
usages of it in the rx path.
drivers/firewire/net.c | 59 ++++++++++++++++++++++++-----------------
1 file changed, 35 insertions(+), 24 deletions(-)
Index: b/drivers/firewire/net.c
===================================================================
--- a/drivers/firewire/net.c
+++ b/drivers/firewire/net.c
@@ -28,8 +28,14 @@
#include <asm/unaligned.h>
#include <net/arp.h>
-#define FWNET_MAX_FRAGMENTS 25 /* arbitrary limit */
-#define FWNET_ISO_PAGE_COUNT (PAGE_SIZE < 16 * 1024 ? 4 : 2)
+/* rx limits */
+#define FWNET_MAX_FRAGMENTS 25 /* arbitrary limit */
+#define FWNET_ISO_PAGE_COUNT (PAGE_SIZE < 16*1024 ? 4 : 2)
+
+/* tx limits */
+#define FWNET_MAX_QUEUED_DATAGRAMS 8 /* should keep AT DMA busy enough */
+#define FWNET_MIN_QUEUED_DATAGRAMS 2
+#define FWNET_TX_QUEUE_LEN FWNET_MAX_QUEUED_DATAGRAMS /* ? */
#define IEEE1394_BROADCAST_CHANNEL 31
#define IEEE1394_ALL_NODES (0xffc0 | 0x003f)
@@ -641,8 +647,6 @@ static int fwnet_finish_incoming_packet(
net->stats.rx_packets++;
net->stats.rx_bytes += skb->len;
}
- if (netif_queue_stopped(net))
- netif_wake_queue(net);
return 0;
@@ -651,8 +655,6 @@ static int fwnet_finish_incoming_packet(
net->stats.rx_dropped++;
dev_kfree_skb_any(skb);
- if (netif_queue_stopped(net))
- netif_wake_queue(net);
return -ENOENT;
}
@@ -784,15 +786,10 @@ static int fwnet_incoming_packet(struct
* Datagram is not complete, we're done for the
* moment.
*/
- spin_unlock_irqrestore(&dev->lock, flags);
-
- return 0;
+ retval = 0;
fail:
spin_unlock_irqrestore(&dev->lock, flags);
- if (netif_queue_stopped(net))
- netif_wake_queue(net);
-
return retval;
}
@@ -892,6 +889,13 @@ static void fwnet_free_ptask(struct fwne
kmem_cache_free(fwnet_packet_task_cache, ptask);
}
+/* Caller must hold dev->lock. */
+static void dec_queued_datagrams(struct fwnet_device *dev)
+{
+ if (--dev->queued_datagrams == FWNET_MIN_QUEUED_DATAGRAMS)
+ netif_wake_queue(dev->netdev);
+}
+
static int fwnet_send_packet(struct fwnet_packet_task *ptask);
static void fwnet_transmit_packet_done(struct fwnet_packet_task *ptask)
@@ -908,7 +912,7 @@ static void fwnet_transmit_packet_done(s
/* Check whether we or the networking TX soft-IRQ is last user. */
free = (ptask->outstanding_pkts == 0 && ptask->enqueued);
if (free)
- dev->queued_datagrams--;
+ dec_queued_datagrams(dev);
if (ptask->outstanding_pkts == 0) {
dev->netdev->stats.tx_packets++;
@@ -979,7 +983,7 @@ static void fwnet_transmit_packet_failed
/* Check whether we or the networking TX soft-IRQ is last user. */
free = ptask->enqueued;
if (free)
- dev->queued_datagrams--;
+ dec_queued_datagrams(dev);
dev->netdev->stats.tx_dropped++;
dev->netdev->stats.tx_errors++;
@@ -1064,7 +1068,7 @@ static int fwnet_send_packet(struct fwne
if (!free)
ptask->enqueued = true;
else
- dev->queued_datagrams--;
+ dec_queued_datagrams(dev);
spin_unlock_irqrestore(&dev->lock, flags);
@@ -1083,7 +1087,7 @@ static int fwnet_send_packet(struct fwne
if (!free)
ptask->enqueued = true;
else
- dev->queued_datagrams--;
+ dec_queued_datagrams(dev);
spin_unlock_irqrestore(&dev->lock, flags);
@@ -1249,6 +1253,15 @@ static netdev_tx_t fwnet_tx(struct sk_bu
struct fwnet_peer *peer;
unsigned long flags;
+ spin_lock_irqsave(&dev->lock, flags);
+
+ /* Can this happen? */
+ if (netif_queue_stopped(dev->netdev)) {
+ spin_unlock_irqrestore(&dev->lock, flags);
+
+ return NETDEV_TX_BUSY;
+ }
+
ptask = kmem_cache_alloc(fwnet_packet_task_cache, GFP_ATOMIC);
if (ptask == NULL)
goto fail;
@@ -1267,9 +1280,6 @@ static netdev_tx_t fwnet_tx(struct sk_bu
proto = hdr_buf.h_proto;
dg_size = skb->len;
- /* serialize access to peer, including peer->datagram_label */
- spin_lock_irqsave(&dev->lock, flags);
-
/*
* Set the transmission type for the packet. ARP packets and IP
* broadcast packets are sent via GASP.
@@ -1291,7 +1301,7 @@ static netdev_tx_t fwnet_tx(struct sk_bu
peer = fwnet_peer_find_by_guid(dev, be64_to_cpu(guid));
if (!peer || peer->fifo == FWNET_NO_FIFO_ADDR)
- goto fail_unlock;
+ goto fail;
generation = peer->generation;
dest_node = peer->node_id;
@@ -1345,7 +1355,8 @@ static netdev_tx_t fwnet_tx(struct sk_bu
max_payload += RFC2374_FRAG_HDR_SIZE;
}
- dev->queued_datagrams++;
+ if (++dev->queued_datagrams == FWNET_MAX_QUEUED_DATAGRAMS)
+ netif_stop_queue(dev->netdev);
spin_unlock_irqrestore(&dev->lock, flags);
@@ -1356,9 +1367,9 @@ static netdev_tx_t fwnet_tx(struct sk_bu
return NETDEV_TX_OK;
- fail_unlock:
- spin_unlock_irqrestore(&dev->lock, flags);
fail:
+ spin_unlock_irqrestore(&dev->lock, flags);
+
if (ptask)
kmem_cache_free(fwnet_packet_task_cache, ptask);
@@ -1415,7 +1426,7 @@ static void fwnet_init_dev(struct net_de
net->addr_len = FWNET_ALEN;
net->hard_header_len = FWNET_HLEN;
net->type = ARPHRD_IEEE1394;
- net->tx_queue_len = 10;
+ net->tx_queue_len = FWNET_TX_QUEUE_LEN;
SET_ETHTOOL_OPS(net, &fwnet_ethtool_ops);
}
--
Stefan Richter
-=====-==-=- =-== -==-=
http://arcgraph.de/sr/
--
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