Re: Burning audio disc literally 30x the system load of data disc
>From: xiphmont@xiph.org (Monty)
>I've found a peculiar behavior in the 2.4.x series (using recent Linux
>SG 3.1.2x) that I have to fix one way or another. I've tried 2.4.20
>as shipped by Debian and my hand-built 2.4.21.
>In short, I've put together an audio editing workstation to replace
>the aging Snotfish. When burning *data* discs, everything is as
>expected; I can burn four discs simultaneously at 52x at ~15% total
>system load (each burner is on its own busmastering controller... just
>in case). The CD burner buffers have never dropped under 95%.
>However, burning *audio* discs, a single audio burn maxes the machine
>out at 16x. Both Athlon 2800+s are near-pegged and the CDROM buffer
>regularly empties (here, burn-free keeps saving things). ps and top
>both indicate all the load is in the kernel, and strace shows cdrecord
>is using the SG ioctl interface. I've not yet investigated further,
>but I'm about to. I'm tossing this out hoping someone has a
>head-start on the problem.
>I think we all agree, especially when demostrated that four 52x data
>discs (true 52x at the rim, as reported by cdrecord) work fine, that
>one reasonably should expect the same performance burning audio. Or
>at least better than this :-)
>The problem can be demonstrated very easily;
>cdrecord dev=0,0,0 speed=0 -pad -data -v -v -data randomverybigdata
>...works swimmingly. No load, no worries, full speed.
>cdrecord dev=0,0,0 speed=0 -pad -data -v -v -audio randomverybigdata
A problem known for a very long time. The reason is that Linux switches
off DMA if the sector size is not a multiple of 512 bytes.
The speed limit depends on the actual hardware and is somewhere between
16x and 40x.
Jörg
--
EMail:joerg@schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
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