amd64 slower than i386 on identical AMD 64 system?

JoaoBR joao at
Wed Mar 15 09:01:49 UTC 2006

On Tuesday 14 March 2006 23:28, Kris Kennaway wrote:
> 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?

for the obvious ... the never-ending-search for better performance
BTW this option is very bad documented and no hint in NOTES that it may not 

> > 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?

without,  SMP kernel but POLLING enabled

> > 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.

well, read again
 I said here that ULE is giving me BETTER performance

> 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.

obvious, but we often do not know all for sure so it's good talking about 

resuming my experience:

 SMP with single dual-core processors on standard MBs are sensitive (crashing 
easily or time-outs) with non polling NICs

SMP with single dual-core processors are randomly crashing when >2GB and <4GB 
on standard MBs

Both issues are not appearing at all when changing the X2 for a standard 
athlon 64 processor, means same hardware, same OS version and kernel

Both issues are also not appearing when using the dual-core running same 
hardware, same os version but UP kernel (only cutting options SMP).

I understand here that amd64 is still not dealing well with dual-cores and 
more than 2GB of RAM


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