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 16:46:15 -0400
on 6/3/04 2:58 PM, Doug Wyatt at email@hidden wrote:
>
Regardless of thread priorities, I believe the kernel queues I/O
>
requests to a device in the order they were made and they cannot be
>
reordered.
>
>
According to one of the authors of the Carbon File Manager, async reads
>
are no better than synchronous reads on X.
Ok this is interesting So during lunch I had the following idea:
The disk drive is FIFO, so the first person that does a read request will
get it. If I analyze my data with applicaion the number of reads that are
happening are going down because Finder is also doing reads and the IO
manager does a principle of FIFO. So if the number of read request you can
do are going down, what else can you do then:
instead of reading blocks of 140Kbytes which I do currently, I gonna need
to read blocks of bigger data for example 2Mbytes at once. Finder in that
case will not start adding more request to the disk because it is waiting
for his first read to be finished..
I will try to implement this theory and let you guys know if that helped but
just posting this here because maybe some else tried this theory and know
for a fact that it could work.
[The ideal solution is that this would be dynamic change the amount of data
you request from the "read" function depending on the time it took last
time.... you can do this by allocating instead 100 blocks of 140KBytes you
allocate one block of the size of 100 *140Kbytes and you move in that block
instead of playing with buffers, I have done this before it is called
VirtualRingBuffer , but first increasing the 140Kbytes to something like
2Mbytes should be first test]
Thanks again for all replying I have a lot of ideas I can try out to solve
this problem. I want to use MACOSX for realtime broadcasting of video
because I just love this system...
Ok back to work
mvo
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