[I/OAT]: Setup the networking subsystem as a DMA client

Attempts to allocate per-CPU DMA channels

Signed-off-by: Chris Leech <christopher.leech@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 0f15e769c6bc4a35110817f38df3a81d910f4ecf..30d021d1a07c8670687e05abb3238772b7aec181 100644 (file)
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -10,6 +10,18 @@ config DMA_ENGINE
          DMA engines offload copy operations from the CPU to dedicated
          hardware, allowing the copies to happen asynchronously.
 
+comment "DMA Clients"
+
+config NET_DMA
+       bool "Network: TCP receive copy offload"
+       depends on DMA_ENGINE && NET
+       default y
+       ---help---
+         This enables the use of DMA engines in the network stack to
+         offload receive copy-to-user operations, freeing CPU cycles.
+         Since this is the main user of the DMA engine, it should be enabled;
+         say Y here.
+
 comment "DMA Devices"
 
 config INTEL_IOATDMA

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f4169bbb60eb8036d021ba64e9270f6b5ffcaabb..b5760c67af9ce6aeeecfa940dec2c721bd91a3bb 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -37,6 +37,7 @@
 #include <linux/config.h>
 #include <linux/device.h>
 #include <linux/percpu.h>
+#include <linux/dmaengine.h>
 
 struct divert_blk;
 struct vlan_group;
@@ -593,6 +594,9 @@ struct softnet_data
        struct sk_buff          *completion_queue;
 
        struct net_device       backlog_dev;    /* Sorry. 8) */
+#ifdef CONFIG_NET_DMA
+       struct dma_chan         *net_dma;
+#endif
 };
 
 DECLARE_PER_CPU(struct softnet_data,softnet_data);

diff --git a/include/net/netdma.h b/include/net/netdma.h
new file mode 100644 (file)
index 0000000..cbfe89d
--- /dev/null
+++ b/include/net/netdma.h
@@ -0,0 +1,38 @@
+/*
+ * Copyright(c) 2004 - 2006 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place - Suite 330, Boston, MA  02111-1307, USA.
+ *
+ * The full GNU General Public License is included in this distribution in the
+ * file called COPYING.
+ */
+#ifndef NETDMA_H
+#define NETDMA_H
+#include <linux/config.h>
+#ifdef CONFIG_NET_DMA
+#include <linux/dmaengine.h>
+
+static inline struct dma_chan *get_softnet_dma(void)
+{
+       struct dma_chan *chan;
+       rcu_read_lock();
+       chan = rcu_dereference(__get_cpu_var(softnet_data.net_dma));
+       if (chan)
+               dma_chan_get(chan);
+       rcu_read_unlock();
+       return chan;
+}
+#endif /* CONFIG_NET_DMA */
+#endif /* NETDMA_H */

diff --git a/net/core/dev.c b/net/core/dev.c
index 4fba549caf29911c42f7674310fa35aaa993a36c..6bfa78c66c2546722dc2a7d309715fbbd1dbe80f 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -115,6 +115,7 @@
 #include <net/iw_handler.h>
 #include <asm/current.h>
 #include <linux/audit.h>
+#include <linux/dmaengine.h>
 
 /*
  *     The list of packet types we will receive (as opposed to discard)
@@ -148,6 +149,12 @@ 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
+static struct dma_client *net_dma_client;
+static unsigned int net_dma_count;
+static spinlock_t net_dma_event_lock;
+#endif
+
 /*
  * The @dev_base list is protected by @dev_base_lock and the rtnl
  * semaphore.
@@ -1846,6 +1853,19 @@ static void net_rx_action(struct softirq_action *h)
                }
        }
 out:
+#ifdef CONFIG_NET_DMA
+       /*
+        * There may not be any more sk_buffs coming right now, so push
+        * any pending DMA copies to hardware
+        */
+       if (net_dma_client) {
+               struct dma_chan *chan;
+               rcu_read_lock();
+               list_for_each_entry_rcu(chan, &net_dma_client->channels, client_node)
+                       dma_async_memcpy_issue_pending(chan);
+               rcu_read_unlock();
+       }
+#endif
        local_irq_enable();
        return;
 
@@ -3300,6 +3320,88 @@ static int dev_cpu_callback(struct notifier_block *nfb,
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
+#ifdef CONFIG_NET_DMA
+/**
+ * net_dma_rebalance -
+ * 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)
+                       rcu_assign_pointer(per_cpu(softnet_data.net_dma, cpu), NULL);
+               unlock_cpu_hotplug();
+               return;
+       }
+
+       i = 0;
+       cpu = first_cpu(cpu_online_map);
+
+       rcu_read_lock();
+       list_for_each_entry(chan, &net_dma_client->channels, client_node) {
+               n = ((num_online_cpus() / net_dma_count)
+                  + (i < (num_online_cpus() % net_dma_count) ? 1 : 0));
+
+               while(n) {
+                       per_cpu(softnet_data.net_dma, cpu) = chan;
+                       cpu = next_cpu(cpu, cpu_online_map);
+                       n--;
+               }
+               i++;
+       }
+       rcu_read_unlock();
+
+       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)
+{
+       spin_lock(&net_dma_event_lock);
+       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;
+       }
+       spin_unlock(&net_dma_event_lock);
+}
+
+/**
+ * netdev_dma_regiser - register the networking subsystem as a DMA client
+ */
+static int __init netdev_dma_register(void)
+{
+       spin_lock_init(&net_dma_event_lock);
+       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
@@ -3353,6 +3455,8 @@ 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);