Linux-audio-dev August 2008

linux-audio-dev@lists.linuxaudio.org

66 participants
41 discussions

[ANN] Realtime priority patch for the linux kernel, jack_capture V0.9.23 and Rollendurcmesserzeitsammler V0.0.4

by Kjetil S. Matheussen

Download from: http://old.notam02.no/arkiv/src/?M=D Realtime priority patch for the linux kernel ============================================ To make sure the Linux kernel is able to grant realtime priority, and full nice and mlock capabailites can still be a little bit inconvenient and/or frustrating. However, this super-tiny patch: http://old.notam02.no/arkiv/src/realtime.diff against the linux source shortcuts all other methods. No more pam, realtime-lsm, rtlimits etc. jack_capture ============ jack_capture is a program for recording soundfiles with jack. Its default operation is to capture whatever sound is going out to your speakers into a file. (But it can do a number of other operations as well...) Changes 0.9.19 -> 0.9.23: *Minor spellings *Check for out of memory *Clean up source a bit *Stop connection thread before closing jack client. *Made --help a tiny bit cleaner *Removed shut down code from the SIGINT signal handler. *Fixed segfault in case jack shuts down. Thanks to Julien Claassen for reporting the bug. (Note that there is also a 0.9.24 release. 0.9.24 has changed internal data representation from lockless ringbuffer to lockless lifo and fifo stacks. (Unmodified lifo/fifo code taken from midishare. (Copyright Grame 1999-2005)) 0.9.24 probably works fine, but it shouldn't be used for important recordings since it hasn't been much tested yet.) Rollendurchmesserzeitsammler v0.0.5 ------------------------------------ The Audio Rollendurchmesserzeitsammler is a conservative garbage collector especially made for running inside an audio DSP thread. New about this release is that I have finally replaced TLSF (http://rtportal.upv.es/rtmalloc/) with a pool-based dynamic memory allocator, which makes allocation using the rollendurchmesserzeitsammler approximately as fast as using custom memory pools. Using the rollendurchmesserzeitsammler should be a lot more convenient than memory pools though, and since memory is not freed manually, but instead is automatically freed in a separate thread, there is a slight chance that using rollendurchmesserzeitsammler instead of custom memory pools could make some DSP code run faster. In non-synthetic benchmarks, I have not been able to see any significant improvement in CPU use because of this compared to using the TLSF allocator. But for programs doing millions of allocations per second, the new memory allocator will probably perform significantly better than TLSF, if it would ever make sense doing so many and frequent allocations of course... Changes 0.0.4 -> 0.0.5 * Implemented a custom pool-based dynamic memory allocater. This new memory allocator is now set as default. To use TLSF instead, set "USE_TLSF=-DUSE_TLSF" in the Makefile before compiling. The following changes are caused by this switch: * Allocating memory is now approx 10 times faster (13 vs. 168 instructions for the allocation itself, but there are some GC overhead too) * The allocator copies used memory only (not just the whole heap). But not always! This was a lot more complicated to to with TLSF so I didn't do that. Note that for the garbage collector to still be hard realtime safe, the programs must ensure that full copies are taken now and then. (There's a change in the API for doing that) * Doing a garbage collection is much faster since the heaps are usually much smaller (because only used memory is copied) and that freeing is 10-20 times faster. * Further improvements for reducing memory overhead and make searching for used mem to be O(log n) instead of O(n) is much simpler now. (this is TODO though) * However 1: In case the code using the garbage collector will continue forever to allocate memory of different sizes, the new dynamic memory allocator could eventually run out of memory even if the program itself doesn't use very much memory. I don't think this is very likely to happen for DSP routines though, and there might even be solutions to fix this problem if it should ever come up. For now, just switching to TLSF fixes the problem. * However 2: in non-synthetic benchmarks, I have not been able to see any practical improvement in CPU use, apart from the slight improvement in CPU available for use in non-realtime threads because taking snapshots usually takes a lot less time now. But for programs doing millions of allocations per second, the new memory allocator will probably perform significantly better than TLSF, if it would ever make sense doing so many allocations of course.

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Linux-audio-dev August 2008