Re: How to get a sustained read speed under OS X
Re: How to get a sustained read speed under OS X
- Subject: Re: How to get a sustained read speed under OS X
- From: Marc Van Olmen <email@hidden>
- Date: Thu, 03 Jun 2004 15:29:44 -0400
on 6/3/04 2:43 PM, Bob Ippolito at email@hidden wrote:
>
> Because it is realtime problem I'm having related to video/audio
>
> stream I
>
> hope I can ask you guys this question:
>
>
>
> How do I get a sustained stream working under OS X, or does OS X
>
> doesn't
>
> provide a mechanism for this?
>
>
>
> I thought it was a matter of getting the read thread the right
>
> priority or
>
> is it better that I use some async reading?
>
>
>
> I need to get a sustained speed of 3.5MBytes/second, this is easy to
>
> do but
>
> as soon I start duplicate a file in the Finder on the same hard disk
>
> I'm
>
> trouble, my read speeds drops very low. On a G5 the problem was worse
>
> then
>
> on a G4 because maybe not so good harddisk.
>
>
Read ahead! You shouldn't need to fiddle with thread priorities or
>
anything.. just make sure that your read ahead buffer is big enough to
>
compensate for the kind of scenarios you expect to see.
>
bob
We are buffering a lot I have a buffer of 35MB, but when I launch in the
Finder a file duplicate of 2 Gbytes, the 35MB buffer for my
3.5MBytes/stream... Runs quickly out of cached memory, so the read is become
very slow.
The machine is a DUAL G5 1.8 with 2 GB Ram and only my application is
running a fresh reboot and as soon I start a finder duplicate the stream
runs out of cached memory. I can simulate the problem with QuickTime Player
where I Play a DV movie, and I launch in the Finder 2 duplicates of 2 bigs
files above > 300Mbytes as soon I do that QuickTime Player will stop playing
the DV movie,
With my application I have similar problem but just gave the QT example as
an indication of the problem. I whish I could do some kind of IO scheduler,
so telling the OS that my reads are more important on this disk then any
other read that is busy on this device,
Cheers,
mvo
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