Am 26.06.20 um 18:58 schrieb Robin Murphy:
On 2020-06-26 16:59, Tomasz Figa wrote:
On Fri, Jun 26, 2020 at 5:48 PM Dafna Hirschfeld
<dafna.hirschfeld@xxxxxxxxxxxxx> wrote:
On 26.06.20 16:03, Tomasz Figa wrote:
On Fri, Jun 26, 2020 at 3:32 PM Robin Murphy <robin.murphy@xxxxxxx> wrote:
Hi Dafna,
On 2020-06-25 18:42, Dafna Hirschfeld wrote:
In the stop_streaming callback 'rkisp1_params_vb2_stop_streaming'
there is no need to release the lock 'config_lock' and then acquire
it again at each iteration when returning all buffers.
This is because the stream is about to end and there is no need
to let the isr access a buffer.
Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx>
---
drivers/staging/media/rkisp1/rkisp1-params.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/drivers/staging/media/rkisp1/rkisp1-params.c b/drivers/staging/media/rkisp1/rkisp1-params.c
index bf006dbeee2d..5169b02731f1 100644
--- a/drivers/staging/media/rkisp1/rkisp1-params.c
+++ b/drivers/staging/media/rkisp1/rkisp1-params.c
@@ -1488,19 +1488,13 @@ static void rkisp1_params_vb2_stop_streaming(struct vb2_queue *vq)
/* stop params input firstly */
spin_lock_irqsave(¶ms->config_lock, flags);
params->is_streaming = false;
- spin_unlock_irqrestore(¶ms->config_lock, flags);
for (i = 0; i < RKISP1_ISP_PARAMS_REQ_BUFS_MAX; i++) {
- spin_lock_irqsave(¶ms->config_lock, flags);
if (!list_empty(¶ms->params)) {
buf = list_first_entry(¶ms->params,
struct rkisp1_buffer, queue);
list_del(&buf->queue);
- spin_unlock_irqrestore(¶ms->config_lock,
- flags);
} else {
- spin_unlock_irqrestore(¶ms->config_lock,
- flags);
break;
}
Just skimming through out of idle curiosity I was going to comment that
if you end up with this pattern:
if (!x) {
//do stuff
} else {
break;
}
it would be better as:
if (x)
break;
//do stuff
However I then went and looked at the whole function and frankly it's a
bit of a WTF. As best I could decipher, this whole crazy loop appears to
be a baroque reinvention of:
list_for_each_entry_safe(¶ms->params, ..., buf) {
list_del(&buf->queue);
vb2_buffer_done(&buf->vb.vb2_buf, VB2_BUF_STATE_ERROR);
}
Hi, indeed this is a much simpler implementation, greping 'return_all_buffers'
I see that many drivers implement it this way.
thanks!
(assuming from context that the list should never contain more than
RKISP1_ISP_PARAMS_REQ_BUFS_MAX entries in the first place)
Or if we want to avoid disabling the interrupts for the whole
iteration, we could use list_splice() to move all the entries of
But this code runs when userspace asks to stop the streaming so I don't
think it is important at that stage to allow the interrupts.
It's generally a good practice to reduce the time spent with
interrupts disabled. Disabling the interrupts prevents the system from
handling external events, including timer interrupts, and scheduling
higher priority tasks, including real time ones. How much the system
runs with interrupts disabled is one of the factors determining the
general system latency.
Right, with the way we handle interrupt affinity on Arm an IRQ can't target multiple CPUs in hardware, so any time spent with IRQs disabled might be preventing other devices' interrupts from being taken even if they're not explicitly affine to the current CPU.
Now that I've looked, it appears that vb2_buffer_done() might end up performing a DMA sync on the buffers, which, if it has to do order-of-megabytes worth of cache maintenance for large frames, is the kind of relatively slow operation that really doesn't want to be done with IRQs disabled (or under a lock at all, ideally) unless it absolutely *has* to be. If the lock is only needed here to protect modifications to the params list itself, then moving the whole list at once to do the cleanup "offline" sounds like a great idea to me.
ok, that might be a problem in v4l2 in general since vb2_buffer_done is actually often used inside an irq handler
Robin.
