diff options
| author | Hans Verkuil <hverkuil@xs4all.nl> | 2010-11-26 06:47:28 -0300 |
|---|---|---|
| committer | Mauro Carvalho Chehab <mchehab@redhat.com> | 2010-12-01 20:10:19 -0200 |
| commit | 879aa24d6394aa04b690a600a41ff500441ad384 (patch) | |
| tree | 024886e8a84ab3f7e88c1e2c5aeceae28cc344bb /drivers/media | |
| parent | 2877842de8cbf6272b0a851cb12587b7dd8c2afb (diff) | |
| download | linux-879aa24d6394aa04b690a600a41ff500441ad384.tar.bz2 | |
[media] V4L: improve the BKL replacement heuristic
The BKL replacement mutex had some serious performance side-effects on
V4L drivers. It is replaced by a better heuristic that works around the
worst of the side-effects.
Read the v4l2-dev.c comments for the whole sorry story. This is a
temporary measure only until we can convert all v4l drivers to use
unlocked_ioctl.
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Diffstat (limited to 'drivers/media')
| -rw-r--r-- | drivers/media/video/v4l2-dev.c | 31 | ||||
| -rw-r--r-- | drivers/media/video/v4l2-device.c | 1 |
2 files changed, 29 insertions, 3 deletions
diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c index bfd392e2436d..6b64fd607b20 100644 --- a/drivers/media/video/v4l2-dev.c +++ b/drivers/media/video/v4l2-dev.c @@ -245,13 +245,38 @@ static long v4l2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg) if (vdev->lock) mutex_unlock(vdev->lock); } else if (vdev->fops->ioctl) { - /* TODO: convert all drivers to unlocked_ioctl */ + /* This code path is a replacement for the BKL. It is a major + * hack but it will have to do for those drivers that are not + * yet converted to use unlocked_ioctl. + * + * There are two options: if the driver implements struct + * v4l2_device, then the lock defined there is used to + * serialize the ioctls. Otherwise the v4l2 core lock defined + * below is used. This lock is really bad since it serializes + * completely independent devices. + * + * Both variants suffer from the same problem: if the driver + * sleeps, then it blocks all ioctls since the lock is still + * held. This is very common for VIDIOC_DQBUF since that + * normally waits for a frame to arrive. As a result any other + * ioctl calls will proceed very, very slowly since each call + * will have to wait for the VIDIOC_QBUF to finish. Things that + * should take 0.01s may now take 10-20 seconds. + * + * The workaround is to *not* take the lock for VIDIOC_DQBUF. + * This actually works OK for videobuf-based drivers, since + * videobuf will take its own internal lock. + */ static DEFINE_MUTEX(v4l2_ioctl_mutex); + struct mutex *m = vdev->v4l2_dev ? + &vdev->v4l2_dev->ioctl_lock : &v4l2_ioctl_mutex; - mutex_lock(&v4l2_ioctl_mutex); + if (cmd != VIDIOC_DQBUF && mutex_lock_interruptible(m)) + return -ERESTARTSYS; if (video_is_registered(vdev)) ret = vdev->fops->ioctl(filp, cmd, arg); - mutex_unlock(&v4l2_ioctl_mutex); + if (cmd != VIDIOC_DQBUF) + mutex_unlock(m); } else ret = -ENOTTY; diff --git a/drivers/media/video/v4l2-device.c b/drivers/media/video/v4l2-device.c index 0b08f96b74a5..7fe6f92af480 100644 --- a/drivers/media/video/v4l2-device.c +++ b/drivers/media/video/v4l2-device.c @@ -35,6 +35,7 @@ int v4l2_device_register(struct device *dev, struct v4l2_device *v4l2_dev) INIT_LIST_HEAD(&v4l2_dev->subdevs); spin_lock_init(&v4l2_dev->lock); + mutex_init(&v4l2_dev->ioctl_lock); v4l2_dev->dev = dev; if (dev == NULL) { /* If dev == NULL, then name must be filled in by the caller */ |