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: Matthew Xavier Mora <email@hidden>
- Date: Thu, 3 Jun 2004 12:47:04 -0700
At 3:29 PM -0400 6/3/04, Marc Van Olmen wrote:
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,
Have you tried file mapping the file and just touch the pages a head
of where you need them? The VM pager has the highest priority I
believe.
Matt
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