Subject: Re: [Fwd: [linux-audio-dev] info point on linux hdr]
From: Benno Senoner (sbenno_AT_gardena.net)
Date: Sat Apr 15 2000 - 01:59:17 EEST
I can only say that I am not using any form of preallocation and still get
acceptable performance, even if I am forced to use quite big buffers to
overcome to filesystem latencies.
I tried to compare ext2 to FAT, but I do not get visible differences in terms of
buffer usage spikes (= disk thread blocks for long time due to the filesystem
being busy).
Therefore I suspect it's not a matter of filesystem ( ext2 or FAT), but buffer
flushing I (update,bdlush) and metadata updating.
Anyway I hope that one day we will be able to simply use O_DIRECT and get
RAW I/O access on a per-file basis, doing directly disk from/to userspace
transfers.
I think that this would help us to greatly reduce the needed buffersizes when
doing audio multitrack recording.
does anyone know if/when this is planned ?
(2.3.x kernels already contain the O_DIRECT define, but it's currently ignored)
PS: Does anyone know how to make a RAW I/O device on a spare disk partition,
and then put an ext2 over it (running the whole partition in RAWIO mode) ?
Is that possible ?
If yes I could run my multitrack benchmarks to see how much we can gain in terms
of needed buffersizes (should get smaller by at least 1/4 or so).
Benno.
On Fri, 14 Apr 2000, Andrew Clausen wrote:
>
> Hi all,
>
> Any comments?
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> From: Paul Barton-Davis <pbd_AT_Op.Net>
> To: linux-audio-dev_AT_ginette.musique.umontreal.ca
> Subject: [linux-audio-dev] info point on linux hdr
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>
> i mentioned in some remarks to benno how important i thought it was to
> preallocate the files used for hard disk recording under linux.
>
> i was doing more work on ardour yesterday, and had the occasion to
> create some new "tapes", of lengths from 2 to 40 minutes.
>
> the simple act of creating 24 5 minute WAV files on ext2, files in
> which every block has been allocated, takes at least 1 minute, perhaps
> as much as 2. i create the files by first opening them, then writing a
> zero byte every blocksize bytes (blocksize comes from stat(2)), except
> for the WAV header at the beginning.
>
> i hadn't done this in a while, but it reminded me of the
> near-impossibility of expecting the FS code to allocate this much disk
> space in real time under ext2. If someone knows of a faster way to
> allocate the disk space, please let me know. Its not that I have a
> problem right now, just wanted to point out this behaviour.
>
> --p
>
>
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