Re: Benchmarking mpsafevfs with parallel tarball extraction

On Fri, May 06, 2005 at 11:48:52AM -0700, 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).
> 
> For some reason I get better performance writing to a filesystem
> mounted on this md:
> 
> # dd if=/dev/zero of=foo bs=1024k count=500
> 500+0 records in
> 500+0 records out
> 524288000 bytes transferred in 7.943042 secs (66005946 bytes/sec)
> # rm foo
> # dd if=/dev/zero of=foo bs=1024k count=500
> 500+0 records in
> 500+0 records out
> 524288000 bytes transferred in 7.126929 secs (73564364 bytes/sec)
> # rm foo
> # dd if=/dev/zero of=foo bs=1024k count=500
> 500+0 records in
> 500+0 records out
> 524288000 bytes transferred in 7.237668 secs (72438804 bytes/sec)
> 
> If the write bandwidth is only 50-70MB/sec, then it won't be hard to
> saturate, so I won't probe the full scalability of mpsafevfs here.

I tried on a quad amd64 machine, which has md bandwidth an order of
magnitude greater, but it has the same limiting concurrency of 2.2, so
something else is happening here.

Kris