Re: [LAU] Simple, easy multithreaded circular buffer library for Linux?

Olivier Guilyardi wrote:
> Paul Coccoli wrote:
>> On Fri, Oct 17, 2008 at 8:46 AM, Paul Davis <paul@email-addr-hidden> wrote:
>>> On Fri, 2008-10-17 at 14:13 +0200, Olivier Guilyardi wrote:
>>>
>>>> Okay, I wrote such a test. It fails with Jack's ringbuffer (jack1 r3004) but
>>>> succeeds with Portaudio's one (r1240).
>>> Nice work. Nobody ask why we didn't do this 5 years ago!
>
> Thanks Paul :)
>
>>>> The Portaudio code looks more and more robust to me. It's also surprisingly
>>>> short. Maybe that the best would be to replace jack's ringbuffer with it? I
>>>> think it should be possible to keep the jack_ringbuffer api unchanged.
>>> I'd rather add the memory barriers to the JACK code, but this could be a
>>> race to see who does what first. A memory barrier is typically single
>>> instruction. The complication tends to be defining them in a
>>> sufficiently portable way.
>>>
>> Why do you suspect you need memory barriers? My concern with
>> ringbuffer.c is the non-atomic ops on the read and write pointers.
>> They're marked volatile, but what I think you really want is make all
>> ops on those fields atomic. Stuff like this:
>
> [...]
>
> As I said, the Portaudio ringbuffer passes the test even with memory barriers
> deactivated. But the lack of memory barriers in jack code was the reason I wrote
> this test, please read the whole thread for links to relevant documents.
>
> Yeah, at PulseAudio they say that the way jack ringbuffer uses volatile is wrong.
>
> Anyway, I've read a lot of different (and very opposed) point of views on these
> matters, and IMO there's nothing like thorough testing to sort this out.
>
> To figure whether memory barriers are needed or not, we need to run the test on
> various architectures.
>
> For this purpose, I've set up a small svn repo with everything to run the test
> easily. There's no dependency, you just need pthread, gcc and sh.
>
> Here's how to run the test:
>
> svn co http://svn.samalyse.com/misc/rbtest
> cd rbtest
> make test
>
> It tests the ringbuffers from (all included) jack, portaudio and portaudio
> without barriers. That can take up to 6 minutes. It has to be a bit long due to
> the probabilistic nature of failures.
>
> LAUsers could you please run this test on various architectures? Especially
> PowerPC single-cpu and SMP, x86 single-cpu, SMP, in various flavors, etc...
>
> Cheers,
>

vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Core(TM)2 CPU T7200 @ 2.00GHz
stepping : 6

Starting ringbuffer tests (buffer size: 512)

=== Jack ringbuffer test ===
starting ringbuffer stress test (2 minutes max)
buffer size (bytes): 512
array size (bytes): 256
reader started on cpu 0
writer started on cpu: 1
48128 != 48000 at offset 0
failure in chunk 971504

=== Portaudio ringbuffer test ===
starting ringbuffer stress test (2 minutes max)
buffer size (bytes): 512
array size (bytes): 256
reader started on cpu 1
writer started on cpu: 0
Success

=== Portaudio ringbuffer test (without memory barriers) ===
starting ringbuffer stress test (2 minutes max)
buffer size (bytes): 512
array size (bytes): 256
reader started on cpu 1
writer started on cpu: 0
Success

It would be great if this got fixed since we (FFADO) exercised the GPL
on the jack ringbuffer code...

Greets,

Pieter
_______________________________________________
Linux-audio-user mailing list
Linux-audio-user@email-addr-hidden
http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
Received on Fri Oct 17 20:15:09 2008