[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>

4 files changed, 158 insertions, 0 deletions

diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 0f15e769c6bc..30d021d1a07c 100644
--- 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 f4169bbb60eb..b5760c67af9c 100644
--- 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
index 000000000000..cbfe89d7e5d0
--- /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 4fba549caf29..6bfa78c66c25 100644
--- 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);