linuxaudio.org

On Fri, Oct 17, 2008 at 04:39:25PM +0200, Olivier Guilyardi wrote:

quoted text
> Paul Coccoli wrote:

> > On Fri, Oct 17, 2008 at 8:46 AM, Paul Davis  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...

cc -Wall -I. -I./jack -lpthread -o test-int-array-jack \

		test-int-array.c jack/ringbuffer.c

test-int-array.c: In function ‘main’:

test-int-array.c:113: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’

cc -Wall -I. -I./portaudio -lpthread -o test-int-array-portaudio \

		test-int-array.c portaudio/ringbuffer.c portaudio/pa_ringbuffer.c

test-int-array.c: In function ‘main’:

test-int-array.c:113: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’

cc -Wall -I. -I./portaudio -lpthread -o test-int-array-portaudio-nobarrier \

		-DNO_MEMORY_BARRIER \

		test-int-array.c portaudio/ringbuffer.c portaudio/pa_ringbuffer.c

test-int-array.c: In function ‘main’:

test-int-array.c:113: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’

cc -Wall -I. -I./jack -lpthread -o test-int-array-jack-fix1 \

		test-int-array.c jack/ringbuffer-fix1.c

test-int-array.c: In function ‘main’:

test-int-array.c:113: warning: format ‘%d’ expects type ‘int’, but argument 2 has type ‘long unsigned int’
./alltests.sh

Starting ringbuffer tests (buffer size: 512)
=== Jack ringbuffer test ===

starting ringbuffer stress test (2 minutes max)

buffer size (bytes): 512

array size (bytes): 256

./alltests.sh: line 9:  7742 Segmentation fault      ./test-int-array-jack $BUFFER_SIZE
=== Jack ringbuffer test (with fix 1) ===

starting ringbuffer stress test (2 minutes max)

buffer size (bytes): 512

array size (bytes): 256

./alltests.sh: line 13:  7745 Segmentation fault      ./test-int-array-jack-fix1 $BUFFER_SIZE
=== Portaudio ringbuffer test ===

starting ringbuffer stress test (2 minutes max)

buffer size (bytes): 512

array size (bytes): 256

./alltests.sh: line 17:  7748 Segmentation fault      ./test-int-array-portaudio $BUFFER_SIZE
=== Portaudio ringbuffer test (without memory barriers) ===

starting ringbuffer stress test (2 minutes max)

buffer size (bytes): 512

array size (bytes): 256

./alltests.sh: line 21:  7751 Segmentation fault      ./test-int-array-portaudio-nobarrier $BUFFER_SIZE

make: *** [test] Error 139
Info on the system this was run on, is here:

http://restivo.nfshost.com/projects/asus/system-details/
-ken

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