Hello
Does anyone know of any possible concerns in moving a "production" CentOS 4 install from one machine to another where the "only" difference is that the processor changes from a 1.8 Intel P4 "without" Hyper-Threading to a 3.0 Intel P4 "with" Hyper-Threading ?
I am guessing not, yet I "have to" ask.
Regards,
- rh
I assume you mean by swapping the harddisk to a new box? That should be fine. If you are not already using an SMP kernel then you might want to install it: yum install kernel-smp
It is optional but might give you better performance because you can use the HT.
John.
Robert Hanson wrote:
Hello
Does anyone know of any possible concerns in moving a "production" CentOS 4 install from one machine to another where the "only" difference is that the processor changes from a 1.8 Intel P4 "without" Hyper-Threading to a 3.0 Intel P4 "with" Hyper-Threading ?
I am guessing not, yet I "have to" ask.
Regards,
- rh
CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
-----Original Message----- From: centos-bounces@centos.org [mailto:centos-bounces@centos.org] On Behalf Of John Newbigin Sent: Tuesday, April 19, 2005 4:16 PM To: CentOS mailing list Subject: Re: [CentOS] CentOS 4 and Intel P4 without Hyper-Threading vs. IntelP4 with Hyper-Threading
I assume you mean by swapping the harddisk to a new box? That should be fine. If you are not already using an SMP kernel then you might want to install it: yum install kernel-smp It is optional but might give you better performance because you can use the HT. John.
***************
Thanks John!
Yes. That is safe to assume. Yet...
Are you saying that the standard stock CentOS 4 kernel does not recognize nor use or take advantage of HT on a stand alone Intel processor and motherboard? This is a 865PERL w/LAN I use for development and testing...
... and that if I upgrade to a SMP kernel on this machine that I will have no problem on a single processor machine/motherboard and HT will then be enabled?
I "seem to" recall posts on this list recently where people were "disabling" HT on their multi-processor Intel boxen because of problems.
Is this the case as well or were they enabling it. I'll see if I can find out yet if anyone can shed info it would be much appreciated.
Basically I am looking at very simple production reliability and testing issues.
TIA
- rh
Robert Hanson wrote:
Are you saying that the standard stock CentOS 4 kernel does not recognize nor use or take advantage of HT on a stand alone Intel processor and motherboard? This is a 865PERL w/LAN I use for development and testing...
There are two "standard" kernels distributed with every Red Hat system (CentOS being clone of RHEL). One without SMP support, and one with SMP support. The reason is that SMP support adds additional overhead to the kernel (access to kernel structures must be locked, and so forth). Most people are running UP machines, and therefore benefit from running kernel that is optimized for UP machines.
If you install CentOS on UP machine, Anaconda (that's the installer) will install only "kernel" package (the kernel optimized for UP machines, no SMP support). If you install CentOS on SMP machine or on UP P4 HT machine, Anaconda will install both "kernel" and "kernel-smp" packages, and make SMP kernel default.
So, to answer you question. Yes. By default it will take advantage if you initally installed it on SMP machine. If you installed on UP machine, and later on moved disks to SMP machine, you need to manually add kernel-smp package (not a big deal, rather trivial to do).
BTW, do note that HT processor still has only single core. Some reports indicate that there's not much advantage of HT over non-HT processors (and consequently not much advantage of running SMP kernel on HT processor). Your "two virtuall" processors are still running on single core. The real thing (dual-core processors) is something Intel has announced to start shipping in near future. Up until now, dual cores were limited to RISC processors such as UltraSPARC and Alpha.
On 4/20/05 9:09 AM, Aleksandar Milivojevic wrote:
BTW, do note that HT processor still has only single core. Some reports indicate that there's not much advantage of HT over non-HT processors (and consequently not much advantage of running SMP kernel on HT processor).
Fully realizing that the plural of "anecdote" is not "data," I can report that enabling HT and running an SMP kernel speeds up parallel make operations by 15-20%. E.g., running "make -j2" on P4/HT/SMP is slightly faster than "make -j2" on the same processor running a UP kernel. It seems like the SMP kernel is better able to keep the core busy than the UP kernel.
Other operations, particularly day-to-day desktop stuff, seemingly don't benefit much at all.
A hyper threaded processor is only a single core CPU.
Its more marketing than performance, however you might as well run an SMP kernel on it just 'cause you can ;-)
When you upgrade to your twin Core Opterons, now that would be a good machine to run an SMP kernel on
P.
Paul Heinlein wrote:
On 4/20/05 9:09 AM, Aleksandar Milivojevic wrote:
BTW, do note that HT processor still has only single core. Some reports indicate that there's not much advantage of HT over non-HT processors (and consequently not much advantage of running SMP kernel on HT processor).
Fully realizing that the plural of "anecdote" is not "data," I can report that enabling HT and running an SMP kernel speeds up parallel make operations by 15-20%. E.g., running "make -j2" on P4/HT/SMP is slightly faster than "make -j2" on the same processor running a UP kernel. It seems like the SMP kernel is better able to keep the core busy than the UP kernel.
Other operations, particularly day-to-day desktop stuff, seemingly don't benefit much at all.
Robert Hanson wrote:
... and that if I upgrade to a SMP kernel on this machine that I will have no problem on a single processor machine/motherboard and HT will then be enabled?
I "seem to" recall posts on this list recently where people were "disabling" HT on their multi-processor Intel boxen because of problems.
For the most part, it is safe to run the UP or the SMP kernel on any machine with or without HT and/or multiple CPUs.
In some rare cases, one kernel or the other will not work as expected (ie. at all) and you might have to supply some boot parameters like noacpi etc. If you do have a problem though, just reboot into the other kernel.
Other people have summarised HT. If you can afford to test it (on a live system) turn it off in the BIOS to be safe (or ignore it and use the UP kernel).
If you do have multiple CPUs or a yet to be released dual core CPU then you probably want to use the SMP kernel or you have hardware sitting idle.
Some poorly written drivers don't like SMP. Everything that comes standard with CentOS should be SMP safe but if you start adding 3rd part drivers, watch out.
John.
-
Aleksandar Milivojevic -
John Newbigin -
Paul Heinlein -
Peter Farrow -
Robert Hanson