JRockit Hyperthreading support on Windows 2000?

Question

I am trying to find out if JRockit 8.0 supports hyperthreading correctly on Windows Server 2000. I know that Win2K doesn't have proper support for hyperthreading in that to support it you need to use additional CPU licences rather than the OS identifying the hyperthreading capability properly. This is not cost efficient as you need additional CPU licences and the OS doesn't schedule threads efficiently when there are multiple CPUs on the server. As it treats 4 hyperthreading capable CPUs as 8 physical processors which isn't correct.
Does JRockit rely on the OS for hyperthreading or does it use its own APIs for handling hyperthreading CPUs?
I assume that it relies on the OS, however I wanted to make sure.
Thanks,
Justin

Answer 1

Justin Hancock said the following on 2004-02-04 14:34:
=?ISO-8859-1?Q?Bj=F6rn_Antonsson?= wrote:
Justin Hancock said the following on 2004-01-29 03:43:
I am trying to find out if JRockit 8.0 supports hyperthreading
correctly on Windows Server 2000. I know that Win2K doesn't have
proper support for hyperthreading in that to support it you need
to use additional CPU licences rather than the OS identifying the
hyperthreading capability properly. This is not cost efficient as
you need additional CPU licences and the OS doesn't schedule threads
efficiently when there are multiple CPUs on the server. As it treats
4 hyperthreading capable CPUs as 8 physical processors which isn't
correct.
Does JRockit rely on the OS for hyperthreading or does it use its
own APIs for handling hyperthreading CPUs?
I assume that it relies on the OS, however I wanted to make sure.
Thanks,
JustinJRockit relies completely on the OS for thread scheduling when
using native threads. There is no way for an application to enable
the hyper threading of a CPU if it isn't enabled at boot time and
recognized by the OS as a physical or logical CPU.
On the other hand, if we detect that the CPU is hyper threading
enabled, which we can do without the help of the OS, we will do
some optimizations that Intel have described on their development
pages to enhance the performance of apps running on hyper threading
hardware.
Hope this answers your question.
/BjörnIf I use a JRockit threads is the hyperthreading capability exploited?> More importantly will performance improve?
>
Thanks,
JustinI am not sure that I understand what you mean here. For hyperthreading
to be exploited, it needs to be recognized by the BIOS and the OS.
If you have a box with 2 physical HT-CPUs that shows up as 4 CPUs in
your OS, then hyperthreading is exploited. There is nothing that an
application can do to change this.
The application can only do small optimizations to the way it behaves
so that it works faster on a HT-system compared to if it didn't do
these optimizations. It can not enable hyperthreading.
Intels rule of thumb for perfomance increases is 20-30% if HT is
enabled compared to if it isn't. This increase is from enabling HT
on your box and making the OS believ that it has double the number
of CPUs.
/Björn