p4 and hyper-threading

WipeOut wipe_out at users.sourceforge.net
Wed Jan 7 21:12:15 UTC 2004


Castelhano, Dan wrote:

>Hello,
>
>Please forgive me if any of you feel this post is a little off topic. 
>
>I have a problem with a Pentium 4 hyper threaded chip running on redhat 7.3
>with all of redhat's errata updates and their latest smp kernel.
>
>I have not tested this PC yet with the fedora release due to time
>constraints, but am hoping someone has a similarly configured pc with the
>same problem, or no problem before I progress further.
>
>The problem is this:
>
>I seem to be unable to make the hyper-threading functionality of my Pentium
>4 3.2ghz processor work. I've searched google and redhat/fedora list
>archives and haven't found a similar post to this problem, so I have no idea
>what is wrong.
>
>*This is an HP system, with the latest BIOS
>*Hyper-threading is enabled in bios
>*Added acpismp=force to my grub boot line (kernel /vmlinuz-2.4.20-28.7smp ro
>root=/dev/hda7 hdc=ide-scsi acpismp=force) - saw a blub somewhere on the net
>to add this to make it work, although it seems to do nothing in my case.
>*Applied every single errata update redhat has for 7.3 
>*Using redhat kernel: kernel-smp-2.4.20-28.7 (uname -a: Linux ---
>2.4.20-28.7smp #1 SMP Thu Dec 18 11:18:31 EST 2003 i686 unknown)
>
>And still top and /proc/cpuinfo list only one processor.
>
>>From my readings and previous experience with the p3 hyperthreaded xeons,
>this should work...but this is my first p4 hyperthreaded chip so I do not
>know what is different. 
>
>Side note: when I was setting up this system, the redhat installer installed
>the smp kernel so it must see something for it to have picked the smp
>kernel, otherwise it would have picked the base non-smp kernel...right? so
>why isn't it reporting anything about a 2nd logical proc?
>
>Does anyone have any other ideas of what I can check/change to make
>hyper-threading work on this p4? Is anyone running fedora with this type of
>chip and seeing the 2 logical processors (unlike me)?
>
>Thanks,
>Dan
>
>
>  
>
IIRC HT support was only added to kernel 2.4.21 and later.. I may be 
wrong on this..

In anycase I have an HT proc on a system running RH9 and when using the 
SMP kernel with no additional switches it identifies both logical procs 
with no problems.. so it looks to me like its simply a case of your 
kernel version just being to old..

To be honest HT does not make any real difference that I could see.. its 
not really worth the effort of the upgrade if you are happy in RH7.3..

Later..





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