amd64 slower than i386 on identical AMD 64 system?

Kris Kennaway kris at
Wed Mar 15 02:28:02 UTC 2006

On Tue, Mar 14, 2006 at 07:14:54PM -0300, JoaoBR wrote:

> I can confirm this too
> SMP amd64s are having constant crashes when running >2GB and <4GB of RAM.
> In order not getting anything wrong I am talking about X2-SMP mono-chip-MBs
> this is not happening on dual-chip-MB with two separate processors.
> I run the same hardware as UP-amd64 and it never crashes
> Since this crashes are more frequent with IPI_PREEMPTION I have now some 
> servers under test running without PREEMPTION at all and appearently the 
> crashes are gone

Right, IPI_PREEMPTION is not stable (nor is it enabled by default).
Why did you decide to use it?

> Overall the amd64-SMP kernels running on X2 processors are extermly sensitive 
> to non polling NICs and are crashing often. The overall performance also is 
> bad. 
> Soon I change this cards into polling ones, seems XL is best, I do not have 
> crashes anymore. 
> Funny that single 64bit AMDs are running fine with non polling NICs even when 
> running a SMP enabled kernel. Soon I put back the X2 ... boom.

Crashing with or without the use of broken kernel options?

> > We've been using ubench and pgbench (since these will be PostgreSQL
> > servers) to test.  We're seeing that the 64b stuff runs just a bit
> > slower.  We're also seeing that the amd64 doesn't seem to scale up
> > to using more than one processor, but that's an issue under investigation
> > (see other thread on this list)
> this I can not confirm, I get SMP X2-amds with ULE and 4BSD running on both 
> cpus, same for dual-chip-MBs
> But I can not say anything about PGSQL at all
> My servers are cache servers in first place and I have some web and mail 
> server running amd64 and the cpu scheduling seems to work well. Overall I 
> have the impression that the ULE scheduler is giving better performance on a 
> machine with more than 2MB/s going through

You need to be very careful when claiming bad performance: ULE is
well-known to perform badly on many workloads.

In summary, you need to rule out whether your issues are resulting
from a poor choice of non-standard kernel options, or are actually
bugs in FreeBSD.

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