Re: [linux-audio-dev] more numbers for multichannel playback

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Subject: Re: [linux-audio-dev] more numbers for multichannel playback
From: Erik de Castro Lopo (erikd_AT_zip.com.au)
Date: Wed Apr 05 2000 - 12:27:08 EEST


Paul Barton-Davis wrote:
>
> >This looks kind of weird to me... The time it takes to read n bytes
> >for T tracks should be something like
> >
> > avg_seek_time * T + n * T / avg_transfer_rate
> >
> >but the above suggests that something completely different is taking
> >place...
>
> Yes, the amount of memory used by the process was growing (the lack of
> munmap to release pages),

This is important. In my experiment I used mmap to map in the data,
processed it and then immediately munmap()ped it.

<snip>

> I am actually deeply troubled by my inability to get more than about
> 10-15MB/sec from my nominally 80MB/sec drives. I don't expect 80, but
> I do expect at least 40. I've tried (with no success) to find a
> standard benchmark to make sure I'm not missing some obvious stuff,
> but when I use the following program with a block size of <anything
> above 256kB> i basically get 10MB/sec. This seems wrong, very wrong.

I had similar results (10-12MB/sec) using read() before I moved
to mmap() and immediately got 100000MB/sec. I then made sure I touched
every page of memory and it dropped back to 27MB/sec. A bit of further
tweaking brought it to 37MB/sec.

I'll have to get my code up on a web page. Give me a couple of days :-).

Cheers,
Erik

-- 
+-------------------------------------------------+
     Erik de Castro Lopo     erikd_AT_zip.com.au
+-------------------------------------------------+
"Software is largely a service industry operating under the persistent 
but unfounded delusion that it is a manufacturing industry."
-- Eric S. Raymond


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