Evening all. I recently swapped out my regular 3.0c for a 30 cap 3.0c and hyperthreading stopped working, windows would boot at stock with HT on but super pi and prime failed instantly and it wouldn't boot at all overclocked with HT on. I thought it might be the processor so I tried a 2.8 prescott and the same thing is happening, although with the prescott it will boot overclocked with HT but everything still fails. I've tried a bios update (asus p4c800e delux) went from 1016 to 1018 but no improvement, and I slackened off my memory timings and tried a load of different core voltages (upto 1.56v) and nothing has worked. Is there anyhitng else in the BIOS that I should tweak? The only other thing I can think of is that around the same time as the first upgrade I re-installed windows, normally I unoverclock my computer when I have to do this, if at the same time I turned HT off would this have done anything to windows to stop it from recognising the second virtual processor? Ta.
I have no idea about this software you are using, but for the BIOS and the OS, there is not much to do. When the BIOS sees you have an HT CPU (via CPUID), it builds a second (duplicate) logical CPU table in the ACPI tables. So, basically, if the BIOS is operating properly, it should give you some message about hyper threading and there just aren't any other settings - the BIOS either does the right thing or it doesn't. The OS reads the ACPI tables and says - oh cool two CPUs, but they are listed as two LOGICAL CPU's not two PHYSICAL CPU's. The only difference for the OS is, it should know these "Two CPU's" use the same cache and therefore when it assigns threads, it should consider cache size and do its best to avoid cache misses. Sooooo - basically, like the BIOS, there aren't any settings - it either recognizes the two CPUs and acts right or it doesn't. You can verify this by going into the HW manager and looking for a 2nd CPU entry or going to the task manager and looking for two CPU usage histories under the performance panel. If you see these things, you know the BIOS and the OS have/are doing their job. I personally have only seen HT working with versions of XP, but it theoretically could work with any ACPI OS ('98, ME, 'W2K, versions of Linux). It may be interesting to note that NT used a different method for describing CPUs (from the BIOS to the OS). It was known as MP (as opposed to ACPI), but it only allowed for PHYSICAL CPU's - thus the OS expects it has a full and separate set of cache for each CPU and makes bad decisions about scheduling tasks. Thus NT actually takes a performance hit when running on an HT system. In short, look in your device manager, if you see two CPU's HT is in fact working and there's nothing much to do. If its not working, then your BIOS is at fault (or the CPU doesn't support it). Oh - as an after thought - if the ACPI tables are not loaded properly (the OS will check the ACPI tables). -if it doesn't like them, it will try to boot in MP mode. If that fails it will try APIC or legacy mode, inwhich case it will not support things like sleep/hibernate and some other important stuff. Anyway, look and see if you have the two processors, if you don't I will try to find out how to tell if you are really in ACPI mode (besides seeing if it will hibernate). I know there is an easy way there someplace. What was I saying about short?
In short if you install windows without HT installed it will have a hissy fit. It doesnt matter what the bios says. It confugures itself on install to only work with one cpu. Same with Linux and other OS's If you dont install them with the support for SMP/SMT it wont work. Though the Prime95 errors are a bit weird as windows should still work. Try re intalling windows adn if that doesnt work I would be looking at RAM.
On many(all?) Intel boards there is an option to enable/disable HT. I'd definitely point to you turning it off when reinstalling Windows as the problem, the OS isn't the most intelligent thing in the world and most likely has no clue what to do with this second processor that's just appeared.
lol - yeah When I say settings I mean you can't turn on "HT support for USB" or turn "HT to Full Power". Its either on or off, there's no configuration. So, trouble shooting is basically looking to see if it is working.
OK, I took what he wrote as meaning that when he turned HT on in the BIOS things stopped working, and when he turned it back off again everything worked - not much point testing if HT is working if it's turned off, or maybe that's just me
I really don't know exactly what he is saying is going on - thats why I basically wrote a - "this is how HT works" post
Thanks for the replies chaps, I liked your HT masterclass riluve. I left memtest running this afternoon and there were no errors after 10 passes so I'll give re-installing a go making sure HT is on. I'm not sure why this is bugging me so much, I know HT gives little real in terms of performance but I paid for HT and I want it. Edit: Is there any way I check to see if I had turned off HT last time I installed windows? Will it say anywhere about APIC/APCI?
My pleasure man. It is unlikely you have accedently turned off HT, but I suppose it is possible. The quickest way to check is CTRL_ALT_DEL and look in the performance window for 2 CPU histories. It took some digging but I found that ACPI bugger in Windows go to ->device manager>compuer. There it should say "ACPI Multi-Processor PC" if you have a Multi-processor system OR an HT system. If your HT support is "off" but you are in ACPI mode, it will say "Advanced Configuration and Power Interface (ACPI) PC". I haven't seen a system in a few years that wasn't running ACPI in windows, so if it isn't in ACPI mode, I don't know what exactly it will say, but it should say something other than ACPI. EDIT: Hummm - curiously, I have found a PC that has never had HT or more than one processor, yet the device manager>computer, reports it as an ACPI Multiprocessor PC. So, I would only trust this to say if ACPI is on or off, the CTRL_ALT_DEL > performance window is the best way to see if HT is on. Also, you can look in the Device manager>processors and see if that lists more than one processor. Oh, wait, another note, I just realized, that system has an OEM, pre-installed version of WINXP, so they may have set it up for multipleprocessors somehow.
It's working now. I decided to start my bi-monthly dust removal session early and when I was putting the fans back in and testing them I noticed the fan on my northbridge cooler wasn't spinning. Tried on the chassis header instead of the CPU header and it span up, just for the hell of it I turned HT back on in the BIOS and super pi, prime and everything else that didn't work previously when HT was on is working again. Northbridge must have been getting too hot or perhaps the dodgy fan header was screwing around with voltages? either way I'm a happy bunny. Thanks for all the help.
