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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-rockchip" Errors-To: linux-rockchip-bounces+linux-rockchip=archiver.kernel.org@lists.infradead.org Hi Tomasz, On Thu, Aug 13, 2020 at 02:50:17PM +0200, Tomasz Figa wrote: > On Thu, Aug 13, 2020 at 12:53 PM Laurent Pinchart wrote: > > On Thu, Aug 13, 2020 at 12:44:35PM +0200, Dafna Hirschfeld wrote: > > > 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 wrote: > > > >>> On 26.06.20 16:03, Tomasz Figa wrote: > > > >>>> On Fri, Jun 26, 2020 at 3:32 PM Robin Murphy wrote: > > > >>>>> 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 > > > >>>>>> --- > > > >>>>>> 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. > > > > Ouch. > > > > > ok, that might be a problem in v4l2 in general since vb2_buffer_done > > > is actually often used inside an irq handler > > > > Correct. The DMA sync should be moved to DQBUF time, there shouldn't be > > any reason to do it in the IRQ handler. I thought this had already been > > fixed :-( > > For reference, there was a patch [1] proposed, but it moved the > synchronization to a wrong place in the sequence, already after the > .buf_finish queue callback, ending up breaking the drivers which need > to access the buffer contents there. > > [1] https://patchwork.linuxtv.org/project/linux-media/patch/1494255810-12672-4-git-send-email-sakari.ailus@linux.intel.com/ I think we need to fix the drivers. We just can't do cache sync in IRQ context by default because a few drivers need to access the buffer contents. Those drivers should instead deffer access to a work queue, and sync explicitly. We could possibly provide helpers for that, making it transparent if a queue flag is set. -- Regards, Laurent Pinchart _______________________________________________ Linux-rockchip mailing list Linux-rockchip@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-rockchip