Olivier Guilyardi wrote: > Paul Coccoli wrote: >> On Fri, Oct 17, 2008 at 8:46 AM, Paul Davis <paul@xxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
