Cached file read performance

Eric Anderson anderson at
Thu Dec 21 21:44:51 PST 2006

On 12/21/06 19:35, Mark Kirkwood wrote:
> I recently did some testing on the performance of cached reads using two 
> (almost identical) systems, one running FreeBSD 6.2PRE and the other 
> running Gentoo Linux - the latter acting as a control. I initially 
> started a thread of the same name on -stable, but it was suggested I 
> submit a mail here.
> My background for wanting to examine this is that I work with developing 
> database software (postgres internals related) and cached read 
> performance is pretty important - since we typically try hard to 
> encourage cached access whenever possible.
> Anyway on to the results: I used the attached program to read a cached 
> 781MB file sequentially and randomly with a specified block size (see 
> below). The conclusion I came to was that our (i.e FreeBSD) cached read 
> performance (particularly for smaller block sizes) could perhaps be 
> improved... now I'm happy to help in any way - the machine I've got 
> running STABLE can be upgraded to CURRENT in order to try out patches 
> (or in fact to see if CURRENT is faster at this already!)...
> Best wishes
> Mark
> ----------------------results-etc---------------------------------
> Machines
> ========
> FreeBSD (6.2-PRERELEASE #7: Mon Nov 27 19:32:33 NZDT 2006):
> - Supermicro P3TDER
> - 2xSL5QL 1.26 GHz PIII
> - 2xKingston PC133 RCC Registered 1GB DIMMS
> - 3Ware 7506 4x Maxtor Plus 9 ATA-133 7200 80G
> - Kernal GENERIC + SMP
> - /etc/malloc.conf -> >aj
> - ufs2 32k blocksize, 4K fragments
> - RAID0 256K stripe using twe driver
> Gentoo (2.6.18-gentoo-r3 ):
> - Supermicro P3TDER
> - 2xSL5QL 1.26 GHz PIII
> - 2xKingston PC133 RCC Registered 1GB DIMMS
> - Promise TX4000 4x Maxtor plus 8 ATA-133 7200 40G
> - default make CFLAGS (-O2 -march-i686)
> - xfs stripe width 2
> - RAID0 256K stripe using md driver (software RAID)
> Given the tests were about cached I/O, the differences in RAID 
> controller and the disks themselves were seen as not significant (indeed 
> booting the FreeBSD box with the Gentoo livecd and running the tests 
> there confirmed this).

[..snip of useful results..]

Aren't you also slightly testing parts of the file system code?  Why not 
(since it is only read-only you are interested in) use FreeBSD's xfs 
support (only in -CURRENT however) and run the tests also?  I'm just 
curious if it would make any difference - I would bet not much of any 


Eric Anderson        Sr. Systems Administrator        Centaur Technology
An undefined problem has an infinite number of solutions.

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