[vlc-devel] [PATCH 3/6] codec/mmal: Rework buffer handling

[Julian Scheel]

This patch reduces the number of required pictures in the picture pool as well
as the number of required buffer headers on the mmal component. If
MMAL_ENCODING_OPAQUE is used as data format the number of buffers which have
to be provided to the components ports are very critical and there is a
relation between the configured number of buffers at the port and the actual
number of buffers which are available at at port at any time.
The previous approach was rather conservative and allocated a lot of extra
buffers to ensure that things are smooth all the time. This has the drawback
of wasting memory though. Especially when adding another mmal element
(deinterlace filter) it would caused a situation where we run out of
resources. This new approach reduces the required resources so that another
mmal component can be added to the chain.

Signed-off-by: Julian Scheel <julian at jusst.de>
---
 modules/codec/mmal.c | 30 ++++++++++++++++--------------
 1 file changed, 16 insertions(+), 14 deletions(-)

diff --git a/modules/codec/mmal.c b/modules/codec/mmal.c
index f60ac7d..687e25b 100644
--- a/modules/codec/mmal.c
+++ b/modules/codec/mmal.c
@@ -39,10 +39,12 @@
 /* This value must match the define in video_output/mmal.c
  * Think twice before changing this. Incorrect values cause havoc.
  */
-#define NUM_ACTUAL_OPAQUE_BUFFERS 40
+#define NUM_ACTUAL_OPAQUE_BUFFERS 22
 
-#define NUM_EXTRA_BUFFERS 10
-#define NUM_OPAQUE_BUFFERS 20
+/* These are only required when combined with image_fx filter. But as they
+ * won't do much harm besides using a few MB GPU memory, keep them always on
+ */
+#define NUM_EXTRA_BUFFERS 5
 
 #define MIN_NUM_BUFFERS_IN_TRANSIT 2
 
@@ -184,7 +186,7 @@ static int OpenDecoder(decoder_t *dec)
     if (sys->opaque) {
         extra_buffers.hdr.id = MMAL_PARAMETER_EXTRA_BUFFERS;
         extra_buffers.hdr.size = sizeof(MMAL_PARAMETER_UINT32_T);
-        extra_buffers.value = NUM_ACTUAL_OPAQUE_BUFFERS - NUM_OPAQUE_BUFFERS;
+        extra_buffers.value = NUM_EXTRA_BUFFERS;
         status = mmal_port_parameter_set(sys->output, &extra_buffers.hdr);
         if (status != MMAL_SUCCESS) {
             msg_Err(dec, "Failed to set MMAL_PARAMETER_EXTRA_BUFFERS on output port (status=%"PRIx32" %s)",
@@ -311,11 +313,11 @@ static int change_output_format(decoder_t *dec)
 
     if (sys->opaque) {
         sys->output->buffer_num = NUM_ACTUAL_OPAQUE_BUFFERS;
-        pool_size = sys->output->buffer_num_recommended + NUM_EXTRA_BUFFERS;
+        pool_size = sys->output->buffer_num_recommended;
     } else {
         sys->output->buffer_num = __MAX(sys->output->buffer_num_recommended,
                 MIN_NUM_BUFFERS_IN_TRANSIT);
-        pool_size = sys->output->buffer_num + NUM_EXTRA_BUFFERS;
+        pool_size = sys->output->buffer_num;
     }
 
     sys->output->buffer_size = sys->output->buffer_size_recommended;
@@ -332,15 +334,17 @@ static int change_output_format(decoder_t *dec)
         sys->output_pool = mmal_pool_create(pool_size, 0);
         msg_Dbg(dec, "Created output pool with %d pictures", sys->output_pool->headers_num);
 
-        dec->i_extra_picture_buffers = sys->output_pool->headers_num;
+        /* we need one picture from vout for each buffer header on the output
+         * port */
+        dec->i_extra_picture_buffers = pool_size;
 
+        /* remove what VLC core reserves as it is part of the pool_size
+         * already */
         if (dec->fmt_in.i_codec == VLC_CODEC_H264)
-            dec->i_extra_picture_buffers -= 16;
+            dec->i_extra_picture_buffers -= 19;
         else
-            dec->i_extra_picture_buffers -= 4;
+            dec->i_extra_picture_buffers -= 3;
 
-        dec->i_extra_picture_buffers = __MAX(dec->i_extra_picture_buffers,
-                MIN_NUM_BUFFERS_IN_TRANSIT + 1);
         msg_Dbg(dec, "Request %d extra pictures", dec->i_extra_picture_buffers);
     }
 
@@ -461,9 +465,7 @@ static picture_t *decode(decoder_t *dec, block_t **pblock)
             ret = (picture_t *)buffer->user_data;
             ret->date = buffer->pts;
 
-            buffer->user_data = NULL;
-            buffer->alloc_size = 0;
-            buffer->data = NULL;
+            mmal_buffer_header_reset(buffer);
             mmal_buffer_header_release(buffer);
         }
 
-- 
2.0.0