suppressing queue notification with queue depth parameter (was: [RFC][PATCH] Queue notify support for virtio block device.)

The following patch allows to suppress virtio queue notification with the number of requests passed as parameter.

Changes from v1:
- code styling,
- parameter "x-queue-depth-suppress-notify" for queue depth adjustment.

repository: /home/vadimr/work/upstream/qemu
branch: master
commit d23a1c2fbd23e3da9a671a35c95324d2c630e4c9

Author: Vadim Rozenfeld<[email protected]>
Date:   Thu Jan 14 08:09:26 2010 +0200

[RFC][PATCH v2] suppressing queue notification with queue depth
parameter

hw/virtio-blk.c +4 -0

index cb1ae1f..93b584d 100644
@@ -28,6 +28,8 @@ typedef struct VirtIOBlock
      char serial_str[BLOCK_SERIAL_STRLEN + 1];
      QEMUBH *bh;
      size_t config_size;
+    unsigned int queue_depth;
+    unsigned int requests;
  } VirtIOBlock;
 
  static VirtIOBlock *to_virtio_blk(VirtIODevice *vdev)

@@ -87,6 +89,8 @@ typedef struct VirtIOBlockReq
      struct VirtIOBlockReq *next;
  } VirtIOBlockReq;
 
+static void virtio_blk_handle_output(VirtIODevice *vdev, VirtQueue
 *vq);
+
  static void virtio_blk_req_complete(VirtIOBlockReq *req, int status)
  {

      VirtIOBlock *s = req->dev;

hw/virtio-blk.c +5 -0

@@ -95,6 +99,11 @@ static void virtio_blk_req_complete(VirtIOBlockReq
 *req, int status)
      virtqueue_push(s->vq,&req->elem, req->qiov.size +
 sizeof(*req->in));
      virtio_notify(&s->vdev, s->vq);
 
+    virtio_blk_handle_output(&s->vdev, s->vq);
+    if (--s->requests == (s->queue_depth - 1)) {
+        virtio_queue_set_notification(s->vq, 1);
+    }
+
      qemu_free(req);

  }

hw/virtio-blk.c +4 -0

@@ -340,6 +349,10 @@ static void virtio_blk_handle_output(VirtIODevice
 *vdev, VirtQueue *vq)
              exit(1);
          }
 
+        if (++s->requests == s->queue_depth) {
+            virtio_queue_set_notification(s->vq, 0);
+        }
+
          req->out = (void *)req->elem.out_sg[0].iov_base;
          req->in = (void *)req->elem.in_sg[req->elem.in_num -

1].iov_base;

hw/virtio-blk.c +1 -0

@@ -502,6 +515,7 @@ VirtIODevice *virtio_blk_init(DeviceState *dev,
 DriveInfo *dinfo)
      s->vdev.reset = virtio_blk_reset;
      s->bs = dinfo->bdrv;
      s->rq = NULL;
+    s->queue_depth = drive_get_queue_depth(dinfo->bdrv);
      if (strlen(ps))
          strncpy(s->serial_str, ps, sizeof(s->serial_str));

else

qemu-config.c +4 -0

index c3203c8..6fcf958 100644
@@ -78,6 +78,10 @@ QemuOptsList qemu_drive_opts = {
          },{
              .name = "readonly",
              .type = QEMU_OPT_BOOL,
+        },{
+            .name = "x-queue-depth-suppress-notify",
+            .type = QEMU_OPT_NUMBER,
+            .help = "number of requests in queueu before suppressing
 notify",
          },
          { /* end if list */ }

      },

sysemu.h +2 -0

index 9d80bb2..6eecbe1 100644
@@ -183,6 +183,7 @@ typedef struct DriveInfo {
      BlockInterfaceErrorAction on_read_error;
      BlockInterfaceErrorAction on_write_error;
      char serial[BLOCK_SERIAL_STRLEN + 1];
+    int queue_depth;
      QTAILQ_ENTRY(DriveInfo) next;
  } DriveInfo;
 

@@ -198,6 +199,7 @@ extern DriveInfo *drive_get_by_id(const char *id);
  extern int drive_get_max_bus(BlockInterfaceType type);
  extern void drive_uninit(DriveInfo *dinfo);
  extern const char *drive_get_serial(BlockDriverState *bdrv);
+extern int drive_get_queue_depth(BlockDriverState *bdrv);
 
  extern BlockInterfaceErrorAction drive_get_on_error(
      BlockDriverState *bdrv, int is_read);

vl.c +12 -0

index b048e89..517d290 100644
@@ -2043,6 +2043,18 @@ const char *drive_get_serial(BlockDriverState
 *bdrv)
      return "\0";
  }
 
+int drive_get_queue_depth(BlockDriverState *bdrv)
+{
+    DriveInfo *dinfo;
+
+    QTAILQ_FOREACH(dinfo,&drives, next) {
+        if (dinfo->bdrv == bdrv)
+            return dinfo->queue_depth;
+    }
+
+    return 1;
+}
+
  BlockInterfaceErrorAction drive_get_on_error(
      BlockDriverState *bdrv, int is_read)

  {