Cached file read performance

[Mark Kirkwood]

Bruce Evans wrote:

> 
> None was attached.
> 

(meaning the c prog yes?) I notice that it is stripped out from the web 
archive... so here's a link:

http://homepages.paradise.net.nz/markir/download/freebsd/readtest.c


>> Machines
>> ========
>> - ufs2 32k blocksize, 4K fragments
>     ^^^^^^^^^^^^^^^^^^
> 
> Try using an unpessimized block size.  Block sizes larger than BKVASIZE
> (default 16K) fragment the buffer cache virtual memory. 

Right - I should have said, I saw a comment to that effect in 
src/sys/sys/param.h, and so I tested with 8K, 16K too, interestingly on 
my system 32K seemed to be faster, even for the bigger files (of course 
- hard to know if it was really significant...).

> However, I
> couldn't see much difference between block sizes of 16, 32 and 64K for
> a small (32MB) md-malloced file system with a simple test program.
> All versions got nearly 1/4 of bandwidth of main memory (800MB/S +-10%
> an an AthlonXP with ~PC3200 memory).  

Cheers

Mark