Just a note here - I see much fewer buffer underruns and more consistent
read-ahead/drop-behind behavior (i.e. no paging of other programs) when
using plain read(), as opposed to mmap(). This is in a video playback
program that pumps 3.6MB/sec!
MP3 datarates are less than 50KB/sec, so I don't really see why they stand
to benefit from mmap()... With mmap() you pay the extra cost of setting
up/tearing down the mapping, and the kernel->user copy is virtually
insignificant anyway (you already are paying for a single copy plus cache
pollution when moving the data from filesystem buffer to sound card DMA
buffer, so a second copy isn't a big deal)...
Regards,
Dan
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