[RFC][PATCH 2/5] I/OAT DMA support and TCP acceleration

Chris Leech
2005-12-21T05:18:18Z

Setup the networking subsystem as a DMA client
Attempts to allocate per-CPU DMA channels

---
dev.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 97 insertions(+)

--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -113,6 +113,7 @@
#include <linux/wireless.h> /* Note : will define WIRELESS_EXT */
#include <net/iw_handler.h>
#endif /* CONFIG_NET_RADIO */
+#include <linux/dmaengine.h>
#include <asm/current.h>

/*
@@ -147,6 +148,12 @@ static DEFINE_SPINLOCK(ptype_lock);
static struct list_head ptype_base[16]; /* 16 way hashed list */
static struct list_head ptype_all; /* Taps */

+#ifdef CONFIG_NET_DMA
+struct dma_client *net_dma_client;
+DEFINE_PER_CPU(struct dma_chan *, net_dma);
+static unsigned int net_dma_count;
+#endif
+
/*
* The @dev_base list is protected by @dev_base_lock and the rtln
* semaphore.
@@ -1708,6 +1715,9 @@ static void net_rx_action(struct softirq
unsigned long start_time = jiffies;
int budget = netdev_budget;
void *have;
+#ifdef CONFIG_NET_DMA
+ struct dma_chan *chan;
+#endif

local_irq_disable();

@@ -1739,6 +1749,14 @@ static void net_rx_action(struct softirq
}
}
out:
+#ifdef CONFIG_NET_DMA
+ /*
+ * There may not be any more sk_buffs comming right now, so push
+ * any pending DMA copies to hardware
+ */
+ list_for_each_entry(chan, &net_dma_client->channels, client_node)
+ dma_async_memcpy_issue_pending(chan);
+#endif
local_irq_enable();
return;

@@ -3171,6 +3189,83 @@ static int dev_cpu_callback(struct notif
}
#endif /* CONFIG_HOTPLUG_CPU */

+#ifdef CONFIG_NET_DMA
+/**
+ * net_dma_reblance -
+ * This is called when the number of channels allocated to the net_dma_client
+ * changes. The net_dma_client tries to have one DMA channel per CPU.
+ */
+static void net_dma_rebalance(void)
+{
+ unsigned int cpu, i, n;
+ struct dma_chan *chan;
+
+ lock_cpu_hotplug();
+
+ if (net_dma_count == 0) {
+ for_each_online_cpu(cpu)
+ per_cpu(net_dma, cpu) = NULL;
+ unlock_cpu_hotplug();
+ return;
+ }
+
+ i = 0;
+ cpu = first_cpu(cpu_online_map);
+
+ list_for_each_entry(chan, &net_dma_client->channels, client_node) {
+ /* cpus_clear(chan->cpumask); */
+ n = ((num_online_cpus() / net_dma_count) + (i < (num_online_cpus() % net_dma_count) ? 1 : 0));
+
+ while(n) {
+ per_cpu(net_dma, cpu) = chan;
+ /* cpu_set(cpu, chan->cpumask); */
+ cpu = next_cpu(cpu, cpu_online_map);
+ n--;
+ }
+ i++;
+ }
+
+ unlock_cpu_hotplug();
+}
+
+/**
+ * netdev_dma_event - event callback for the net_dma_client
+ * @client: should always be net_dma_client
+ * @chan:
+ * @event:
+ */
+static void netdev_dma_event(struct dma_client *client, struct dma_chan *chan, enum dma_event event)
+{
+ switch (event) {
+ case DMA_RESOURCE_ADDED:
+ net_dma_count++;
+ net_dma_rebalance();
+ break;
+ case DMA_RESOURCE_REMOVED:
+ net_dma_count--;
+ net_dma_rebalance();
+ break;
+ default:
+ break;
+ }
+}
+
+/**
+ * netdev_dma_register - register the networking subsystem as a DMA client
+ */
+static int __init netdev_dma_register(void)
+{
+ net_dma_client = dma_async_client_register(netdev_dma_event);
+ if (net_dma_client == NULL)
+ return -ENOMEM;
+
+ dma_async_client_chan_request(net_dma_client, num_online_cpus());
+ return 0;
+}
+
+#else
+static int __init netdev_dma_register(void) { return -ENODEV; }
+#endif /* CONFIG_NET_DMA */

/*
* Initialize the DEV module. At boot time this walks the device list and
@@ -3224,6 +3319,8 @@ static int __init net_dev_init(void)
atomic_set(&queue->backlog_dev.refcnt, 1);
}

+ netdev_dma_register();
+
dev_boot_phase = 0;

open_softirq(NET_TX_SOFTIRQ, net_tx_action, NULL);