[pulseaudio-discuss] [PATCH v7] pipe-source: implement autosuspend option

[Raman Shishniou]

On 02/20/2018 04:18 PM, Georg Chini wrote:
> On 20.02.2018 13:50, Raman Shishniou wrote:
>> On 02/20/2018 03:16 PM, Georg Chini wrote:
>>> On 20.02.2018 13:11, Georg Chini wrote:
>>>> On 19.02.2018 16:01, Raman Shyshniou wrote:
>>>>> Currently the pipe-source will remain running even if no
>>>>> writer is connected and therefore no data is produced.
>>>>> This patch adds the autosuspend=<bool> option to prevent this.
>>>>> Source will stay suspended if no writer is connected.
>>>>> This option is enabled by default.
>>>>> ---
>>>>> +
>>>>> +    pa_memchunk_reset(&chunk);
>>>>> +    chunk.memblock = pa_memblock_new(u->core->mempool, u->pipe_size);
>>>> Further down, you might put some data in the memchunk before the
>>>> read if the previous data was not frame aligned, therefore the memblock
>>>> size must be u->pipe_size + fs.
>>> Looking twice, I see you subtract the index from the read size. Nevertheless I
>>> guess it would be simpler to increase the memblock size by one frame.
>> I prefer to keep buffer sizes to be power of 2.
>> Currently pipe_size is 4096 (as determined by pulseaudio, actually 64k,
>> I'll check later why). Adding one frame to the size of buffer makes it
>> a little more than 4096 but much less then 8192> What is the advantage of keeping the buffer size a power of 2?
> What if you have for example a channel count that is not a power
> of 2? Would it not make more sense to keep the buffers frame
> aligned? Anyway, I don't mind if you want to keep it your way.

Usually memory is provided by pages, which is 4096 for x86/x86_64.
Pipe size in linux is one page or 16 pages by default:
http://man7.org/linux/man-pages/man7/pipe.7.html

So the whole page will be used to store one extra frame which is
128 bytes (PA_CHANNELS_MAX * 4 bytes) maximum.

I didn't read pa_memblock_new() code and may be it does not return
page aligned memory. But I believe this is a good practice to keep
page boundaries if possible.

If you look again, the memblock always is frame aligned too.

--
Raman