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media: vivid: fix (partially) timing issues 

The vivid driver is a bit flaky w.r.t. the kthread timing, esp. when
running inside a virtual machine.

This is caused by calling schedule_timeout_uninterruptible(1) which can
actually take more than one jiffie. A while loop with schedule() turns out
to be a lot more precise. Also, if mutex_trylock() fails, then just call
schedule() instead of schedule_timeout_uninterruptible(1). There is no need
to wait until the next jiffer, just schedule(), then try to get the lock
again.

This is still not precise enough, it is still relatively easy to get missed
frames. This really should be converted to use a proper timer, but for now
this solves the worst problems.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Hans Verkuil 2020-10-02 16:48:03 +02:00 committed by Mauro Carvalho Chehab
parent 5e3a81d42e
commit 6e8c09bb8d
4 changed files with 16 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
drivers/media/test-drivers/vivid/vivid-kthread-cap.c
View File

@ -819,7 +819,7 @@ static int vivid_thread_vid_cap(void *data)
break;
if (!mutex_trylock(&dev->mutex)) {
schedule_timeout_uninterruptible(1);
schedule();
continue;
}
@ -888,7 +888,9 @@ static int vivid_thread_vid_cap(void *data)
next_jiffies_since_start = jiffies_since_start;
wait_jiffies = next_jiffies_since_start - jiffies_since_start;
schedule_timeout_interruptible(wait_jiffies ? wait_jiffies : 1);
while (jiffies - cur_jiffies < wait_jiffies &&
!kthread_should_stop())
schedule();
}
dprintk(dev, 1, "Video Capture Thread End\n");
return 0;

6
drivers/media/test-drivers/vivid/vivid-kthread-out.c
View File

@ -167,7 +167,7 @@ static int vivid_thread_vid_out(void *data)
break;
if (!mutex_trylock(&dev->mutex)) {
schedule_timeout_uninterruptible(1);
schedule();
continue;
}
@ -233,7 +233,9 @@ static int vivid_thread_vid_out(void *data)
next_jiffies_since_start = jiffies_since_start;
wait_jiffies = next_jiffies_since_start - jiffies_since_start;
schedule_timeout_interruptible(wait_jiffies ? wait_jiffies : 1);
while (jiffies - cur_jiffies < wait_jiffies &&
!kthread_should_stop())
schedule();
}
dprintk(dev, 1, "Video Output Thread End\n");
return 0;

6
drivers/media/test-drivers/vivid/vivid-kthread-touch.c
View File

@ -69,7 +69,7 @@ static int vivid_thread_touch_cap(void *data)
break;
if (!mutex_trylock(&dev->mutex)) {
schedule_timeout_uninterruptible(1);
schedule();
continue;
}
cur_jiffies = jiffies;
@ -128,7 +128,9 @@ static int vivid_thread_touch_cap(void *data)
next_jiffies_since_start = jiffies_since_start;
wait_jiffies = next_jiffies_since_start - jiffies_since_start;
schedule_timeout_interruptible(wait_jiffies ? wait_jiffies : 1);
while (jiffies - cur_jiffies < wait_jiffies &&
!kthread_should_stop())
schedule();
}
dprintk(dev, 1, "Touch Capture Thread End\n");
return 0;

6
drivers/media/test-drivers/vivid/vivid-sdr-cap.c
View File

@ -142,7 +142,7 @@ static int vivid_thread_sdr_cap(void *data)
break;
if (!mutex_trylock(&dev->mutex)) {
schedule_timeout_uninterruptible(1);
schedule();
continue;
}
@ -201,7 +201,9 @@ static int vivid_thread_sdr_cap(void *data)
next_jiffies_since_start = jiffies_since_start;
wait_jiffies = next_jiffies_since_start - jiffies_since_start;
schedule_timeout_interruptible(wait_jiffies ? wait_jiffies : 1);
while (jiffies - cur_jiffies < wait_jiffies &&
!kthread_should_stop())
schedule();
}
dprintk(dev, 1, "SDR Capture Thread End\n");
return 0;