virtio-net: Make tx_timer timeout configurable

Add an option to make the TX mitigation timer adjustable as a device
option.  The 150us hard coded default used currently is reasonable,
but may not be suitable for all workloads, this gives us a way to
adjust it using a single binary.  We can't support any random option
though, so use the "x-" prefix to indicate this is a developer
option.  Usage:

-device virtio-net-pci,x-txtimer=500000,... # .5ms timeout

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/s390-virtio-bus.c

@@ -27,6 +27,7 @@
 #include "elf.h"
 #include "hw/virtio.h"
 #include "hw/virtio-serial.h"
+#include "hw/virtio-net.h"
 #include "hw/sysbus.h"
 #include "kvm.h"
 
@@ -110,7 +111,7 @@ static int s390_virtio_net_init(VirtIOS390Device *dev)
 {
     VirtIODevice *vdev;
 
-    vdev = virtio_net_init((DeviceState *)dev, &dev->nic);
+    vdev = virtio_net_init((DeviceState *)dev, &dev->nic, &dev->net);
     if (!vdev) {
         return -1;
     }
@@ -327,6 +328,8 @@ static VirtIOS390DeviceInfo s390_virtio_net = {
     .qdev.size = sizeof(VirtIOS390Device),
     .qdev.props = (Property[]) {
         DEFINE_NIC_PROPERTIES(VirtIOS390Device, nic),
+        DEFINE_PROP_UINT32("x-txtimer", VirtIOS390Device,
+                           net.txtimer, TX_TIMER_INTERVAL),
         DEFINE_PROP_END_OF_LIST(),
     },
 };

hw/s390-virtio-bus.h

@@ -43,6 +43,7 @@ typedef struct VirtIOS390Device {
     uint32_t host_features;
     /* Max. number of ports we can have for a the virtio-serial device */
     uint32_t max_virtserial_ports;
+    virtio_net_conf net;
 } VirtIOS390Device;
 
 typedef struct VirtIOS390Bus {

hw/syborg_virtio.c

@@ -68,6 +68,7 @@ typedef struct {
     uint32_t id;
     NICConf nic;
     uint32_t host_features;
+    virtio_net_conf net;
 } SyborgVirtIOProxy;
 
 static uint32_t syborg_virtio_readl(void *opaque, target_phys_addr_t offset)
@@ -284,7 +285,7 @@ static int syborg_virtio_net_init(SysBusDevice *dev)
     VirtIODevice *vdev;
     SyborgVirtIOProxy *proxy = FROM_SYSBUS(SyborgVirtIOProxy, dev);
 
-    vdev = virtio_net_init(&dev->qdev, &proxy->nic);
+    vdev = virtio_net_init(&dev->qdev, &proxy->nic, &proxy->net);
     return syborg_virtio_init(proxy, vdev);
 }
 
@@ -295,6 +296,8 @@ static SysBusDeviceInfo syborg_virtio_net_info = {
     .qdev.props = (Property[]) {
         DEFINE_NIC_PROPERTIES(SyborgVirtIOProxy, nic),
         DEFINE_VIRTIO_NET_FEATURES(SyborgVirtIOProxy, host_features),
+        DEFINE_PROP_UINT32("x-txtimer", SyborgVirtIOProxy,
+                           net.txtimer, TX_TIMER_INTERVAL),
         DEFINE_PROP_END_OF_LIST(),
     }
 };

hw/virtio-net.c

@@ -36,6 +36,7 @@ typedef struct VirtIONet
     VirtQueue *ctrl_vq;
     NICState *nic;
     QEMUTimer *tx_timer;
+    uint32_t tx_timeout;
     int tx_timer_active;
     uint32_t has_vnet_hdr;
     uint8_t has_ufo;
@@ -702,7 +703,7 @@ static void virtio_net_handle_tx(VirtIODevice *vdev, VirtQueue *vq)
         virtio_net_flush_tx(n, vq);
     } else {
         qemu_mod_timer(n->tx_timer,
-                       qemu_get_clock(vm_clock) + TX_TIMER_INTERVAL);
+                       qemu_get_clock(vm_clock) + n->tx_timeout);
         n->tx_timer_active = 1;
         virtio_queue_set_notification(vq, 0);
     }
@@ -842,7 +843,7 @@ static int virtio_net_load(QEMUFile *f, void *opaque, int version_id)
 
     if (n->tx_timer_active) {
         qemu_mod_timer(n->tx_timer,
-                       qemu_get_clock(vm_clock) + TX_TIMER_INTERVAL);
+                       qemu_get_clock(vm_clock) + n->tx_timeout);
     }
     return 0;
 }
@@ -903,7 +904,8 @@ static void virtio_net_vmstate_change(void *opaque, int running, int reason)
     virtio_net_set_status(&n->vdev, n->vdev.status & status);
 }
 
-VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf)
+VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,
+                              virtio_net_conf *net)
 {
     VirtIONet *n;
 
@@ -931,6 +933,7 @@ VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf)
 
     n->tx_timer = qemu_new_timer(vm_clock, virtio_net_tx_timer, n);
     n->tx_timer_active = 0;
+    n->tx_timeout = net->txtimer;
     n->mergeable_rx_bufs = 0;
     n->promisc = 1; /* for compatibility */
 

hw/virtio-net.h

@@ -49,6 +49,11 @@
 
 #define TX_TIMER_INTERVAL 150000 /* 150 us */
 
+typedef struct virtio_net_conf
+{
+    uint32_t txtimer;
+} virtio_net_conf;
+
 /* Maximum packet size we can receive from tap device: header + 64k */
 #define VIRTIO_NET_MAX_BUFSIZE (sizeof(struct virtio_net_hdr) + (64 << 10))
 

hw/virtio-pci.c

@@ -107,6 +107,7 @@ typedef struct {
 #endif
     /* Max. number of ports we can have for a the virtio-serial device */
     uint32_t max_virtserial_ports;
+    virtio_net_conf net;
 } VirtIOPCIProxy;
 
 /* virtio device */
@@ -613,7 +614,7 @@ static int virtio_net_init_pci(PCIDevice *pci_dev)
     VirtIOPCIProxy *proxy = DO_UPCAST(VirtIOPCIProxy, pci_dev, pci_dev);
     VirtIODevice *vdev;
 
-    vdev = virtio_net_init(&pci_dev->qdev, &proxy->nic);
+    vdev = virtio_net_init(&pci_dev->qdev, &proxy->nic, &proxy->net);
 
     vdev->nvectors = proxy->nvectors;
     virtio_init_pci(proxy, vdev,
@@ -690,6 +691,8 @@ static PCIDeviceInfo virtio_info[] = {
             DEFINE_PROP_UINT32("vectors", VirtIOPCIProxy, nvectors, 3),
             DEFINE_VIRTIO_NET_FEATURES(VirtIOPCIProxy, host_features),
             DEFINE_NIC_PROPERTIES(VirtIOPCIProxy, nic),
+            DEFINE_PROP_UINT32("x-txtimer", VirtIOPCIProxy,
+                               net.txtimer, TX_TIMER_INTERVAL),
             DEFINE_PROP_END_OF_LIST(),
         },
         .qdev.reset = virtio_pci_reset,

hw/virtio.h

@@ -185,7 +185,9 @@ void virtio_bind_device(VirtIODevice *vdev, const VirtIOBindings *binding,
 
 /* Base devices.  */
 VirtIODevice *virtio_blk_init(DeviceState *dev, BlockConf *conf);
-VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf);
+struct virtio_net_conf;
+VirtIODevice *virtio_net_init(DeviceState *dev, NICConf *conf,
+                              struct virtio_net_conf *net);
 VirtIODevice *virtio_serial_init(DeviceState *dev, uint32_t max_nr_ports);
 VirtIODevice *virtio_balloon_init(DeviceState *dev);
 #ifdef CONFIG_LINUX