Re: Desktop Filesystem Benchmarks in 2.6.3

[Hans Reiser]

Unfortunately it is a bit more complex, and the truth is less 
complementary to us than what you write.  Reiser4's CPU usage has come 
down a lot, but it still consumes more CPU than V3.  It should consume 
less, and Zam is currently working on making writes more CPU efficient.  
As soon as I get funding from somewhere and can stop worrying about 
money, I will do a complete code review, and CPU usage will go way 
down.  There are always lots of stupid little things that consume a lot 
of CPU that I find whenever I stop chasing money and review code.

We are shipping because CPU usage is not as important as IO efficiency 
for a filesystem, and while Reiser4 is not as fast as it will be in 3-6 
months, it is faster than anything else available so it should be shipped.

Hans

Dax Kelson wrote:

> On Tue, 2004-03-02 at 09:34, Peter Nelson wrote:
>  
>
> > Hans Reiser wrote:
> >
> > I'm confused as to why performing a benchmark out of cache as opposed to 
> > on disk would hurt performance?
> >    
>
> My understanding (which could be completely wrong) is that reieserfs v3
> and v4 are algorithmically more complex than ext2 or ext3. Reiserfs
> spends more CPU time to make the eventual ondisk operations more
> efficient/faster.
>
> When operating purely or mostly out of ram, the higher CPU utilization
> of reiserfs hurts performance compared to ext2 and ext3.
>
> When your system I/O utilization exceeds cache size and your disks
> starting getting busy, the CPU time previously invested by reiserfs pays
> big dividends and provides large performance gains versus more
> simplistic filesystems.  
>
> In other words, the CPU penalty paid by reiserfs v3/v4 is more than made
> up for by the resultant more efficient disk operations. Reiserfs trades 
> CPU for disk performance.
>
> In a nutshell, if you have more memory than you know what do to with,
> stick with ext3. If you spend all your time waiting for disk operations
> to complete, go with reiserfs.
>
> Dax Kelson
> Guru Labs
>
>
>
>  


--
Hans


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