Benchmarking mpsafevfs with parallel tarball extraction

Allen bsdlists at rfnj.org
Fri May 6 12:05:56 PDT 2005


At 14:48 5/6/2005, Kris Kennaway wrote:
>On Fri, May 06, 2005 at 11:35:29AM -0700, Kris Kennaway wrote:
>
> > I might be bumping into the bandwidth of md here - when I ran less
> > rigorous tests with lower concurrency of extractions I seemed to be
> > getting marginally better performance (about an effective concurrency
> > of 2.2 for both 3 and 10 simultaneous extractions - so at least it
> > doesn't seem to degrade badly).  Or this might be reflecting VFS lock
> > contention (which there is certainly a lot of, according to mutex
> > profiling traces).
>
>I suspect that I am hitting the md bandwidth:
>
># dd if=/dev/zero of=/dev/md0 bs=1024k count=500
>500+0 records in
>500+0 records out
>524288000 bytes transferred in 9.501760 secs (55177988 bytes/sec)
>
>which is a lot worse than I expected (even for a 400MHz CPU).

That looks pretty goofy.  Even PC66 SDRAM should be able to push ~250MB/s 
on a very slow processor.  Does the md code for raw access really load this 
much work onto the CPU??


>For some reason I get better performance writing to a filesystem
>mounted on this md:

Part of me wants to think that maybe this is due to some fashion of 
metadata caching, in the manner of softupdates.  Possible?




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