[ecasound] Improving low latency performance

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Subject: [ecasound] Improving low latency performance
From: Kai Vehmanen (k@eca.cx)
Date: Sun Nov 19 2000 - 15:53:22 EET


Ecasound is used as an example in this Dave Phillips' article at O'Reilly
Network. Even without the ecasound references, it'd still be a great
arcticle! ;) Seriously, it's a good introduction to low latency issues
including patching kernels, use of realtime scheduling, disk tuning, etc.

On the 4th page of the article, Dave has noted one important thing
concerning ecasound:

"Andrew Morton suggested that I repeat these tests using an unpatched
2.4.0-test9 kernel with untuned drives. I did, and the results were quite
"Ecasound was the most severely affected, even with the real-time priority
flag set, probably due to the nature of the test (CD-quality stereo
recording). The program reported multiple under-runs through the ALSA PCM
device (/dev/pcmC0D0), and the resulting WAV file was ruined by sixteen
dropouts in a three-minute recording."

This is the very reason why I'm currently concentrating my efforts to
the new double-buffering system. My goal is to achieve reliable
streaming even with standard (no ll-patches) kernel. This means
ecasound has to manage both scheduling and disk i/o latency peaks
upto 300-400ms.

 . http://www.eca.cx ... [ audio software for linux ] /\ . 
 . http://www.eca.cx/sculpscape [ my armchair-tunes mp3/ra/wav ]

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