File I/O with SMP on FreeBSD 4.11 slow

[Kris Kennaway]

On Sun, Sep 18, 2005 at 02:12:05PM +1200, Nikolai Schupbach wrote:
> Hello,
> 
> We have installed FreeBSD 4.11 with SMP enabled in our kernel on a dual Intel
> Xeon 3.2 EMT64 server. We have found file operations like untaring the ports
> tree, or copying directories with many files extremely slow. However if we
> disable SMP support and run on a single CPU the performance is fast.
> 
> Using iostat the performance to untar ports tree is around 4Mb/sec with an SMP
> kernel. Without SMP iostat reports around 50Mb/sec.
> 
> Is this normal for 4.11? We tired SMP on 5.4 and it did not suffer from this
> problem, but we had to revert to 4.11 for other performance reasons.
> 
> Are we better off to run without SMP?

As is well known, SMP support on FreeBSD 4.x was rudimentary, and
performance is poor when two processes are both performing tasks that
require entering the kernel.  This has been a major focus of
development in the FreeBSD 5 branch and beyond, so if SMP performance
is important to you you definitely want the latest release (or wait
for the forthcoming FreeBSD 6.0).

Kris
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