When I built my home machine, I specifically bought an i5 to avoid hyperthreading. On this MBP, it's an i7 and I'm getting slowdowns because hyperthreading is on.

Does anyone here run with it off? If so, how did you turn it off and how do you get it to stay off?

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What makes you think that hyperthreading is slowing down your computer?

I'm running some apps that are not multi-core aware. HT makes the OS think there's more logical cores, so it can spread the load. This works well for non-CPU intensive apps. However, I'm maxing out the logical core, and thus want to halv the logical cores so I can take more advantage of the physical cores. On a PC, I can do this in the BIOS, and have done it before to gain performance. Just haven't had a Mac with HT before.

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I've been meaning to test what MAVIC is posting about for some time now. Just to see the time difference in Handbrake with HT on and off.

When I see HB using 790% of my 4 cores/8 HT threads, I just smile bemusedly wondering what that actually means in terms of performance.

Are you trying to get your non-HT aware apps to run a single thread faster via Turbo Boost?

I know you can have some number of cores run faster (higher clock rate) via Turbo Boost, but you cannot run all cores with Turbo Boost at the same time so in this regard what you are asking seems to make sense to me.

I don't really care about Turbo Boos. Instead of having eight cores, and one being maxed out, I'd rather have four cores and one maxed out.

Lew, when we're talking about HT, 790% with 8 cores is the same as 395% of 4 cores. And, FWIW, one test I found shows that Handbrake, even though it's multi-core aware, runs faster with HT off.

I want the app to take full advantage of the physical core, whereas HT is limiting it so it can only partially use the core.

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found via Google:

Download and install Xcode. It includes a Processor.prefPane (not sure where it's located exactly) that allows you to disable hyperthreading.

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decay, that was apparently killed off in 10.7. As per an apple discussion post where the user called Apple, they said the ability has been removed in 10.7.

I have Xcode installed. I've searched for that prefpane... it's not there.

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Install 10.6 in another boot partition when you have to run that particular single threaded app?

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Unfortunately, I'm going to have to be using that app a lot so rebooting isn't much of an option.

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Don't know if this will work but you use to be able to set the number of active cores from the command line using the nvram command. Here is how:

Developer

Every post I've seen someone give that an answer, someone with 10.7 or 10.8 follows up saying it no longer works.

I've been waiting for this app to startup for 10 minutes...

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have you tried the command line ?

i didn't see if you had done it or not.

. . . you can permanently disable hyperthreading by issuing the following command in the Terminal:

sudo nvram SMT=0

To re-enable hyperthreading, use the command:

sudo nvram -d SMT

Changes take place on a reboot . . .

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Quote
M A V I C
Lew, when we're talking about HT, 790% with 8 cores is the same as 395% of 4 cores. And, FWIW, one test I found shows that Handbrake, even though it's multi-core aware, runs faster with HT off.

Cool, thx! I will definitely be trying this out tonight. I have no need for 8 cores and the only time I come even close to using 4 cores is with HB (which is used a lot). Since my machine doesn't sleep at all or get restarted often, the command line turn-off will probably work for me.

Quote
M A V I C
decay, that was apparently killed off in 10.7. As per an apple discussion post where the user called Apple, they said the ability has been removed in 10.7.

I have Xcode installed. I've searched for that prefpane... it's not there.

First off, you can disable Hyperthreading after installing Xcode by opening the Instruments app from Applications/Xcode/Contents/Applications. Hit Cancel, open Preferences and uncheck Hardware Multi-Threading. This does not stick after a reboot but just pop this in your Dock and it's a quick workaround.

Second: Handbrake runs faster with Hyperthreading on. I converted a 1280x720 hi bitrate movie from my T1i to a lower bitrate using Handbrake's RF20 setting with my custom h.264 string:

HT on: 20.74 fps
HT off: 18.75 fps

Handbrake is faster by ~10% with HT on. I will continue to use it that way.

Quote
M A V I C
I've been waiting for this app to startup for 10 minutes...

That's been your problem?!

That's not a hyperthreading problem.

In fact, Intel licked hyperthreading slowdowns a few years ago. The i7 processors are consistently faster than i5s. (Note that hyperthreading does consume more power, so is considered less efficient in that respect.)

'Seems that you need some traditional troubleshooting. What app are you having trouble with?

...

Edit: Also, your results with Handbrake are way off. Based upon what you've revealed thus far, I suspect that you've got hard drive problems.



Edited 1 time(s). Last edit at 01/08/2013 06:13AM by Chakravartin.

Quote
Lew Zealand
First off, you can disable Hyperthreading after installing Xcode by opening the Instruments app from Applications/Xcode/Contents/Applications. Hit Cancel, open Preferences and uncheck Hardware Multi-Threading. This does not stick after a reboot but just pop this in your Dock and it's a quick workaround.

Sweet, thanks. Every report I've seen for that, said to use a different app that doesn't exist in 10.7.

Quote

Second: Handbrake runs faster with Hyperthreading on. I converted a 1280x720 hi bitrate movie from my T1i to a lower bitrate using Handbrake's RF20 setting with my custom h.264 string:

HT on: 20.74 fps
HT off: 18.75 fps

Handbrake is faster by ~10% with HT on. I will continue to use it that way.

Glad it works faster for you. In the review I found, I don't recall the exact times but it was something like with HT on it took 5:45 and without it it took 5:00.

Quote
Chakravartin
That's been your problem?!

Not the only problem, but related.

Quote

That's not a hyperthreading problem.

Yes, yes it is. On PCs, users have turned off HT to speed things up.

Quote

In fact, Intel licked hyperthreading slowdowns a few years ago. The i7 processors are consistently faster than i5s. (Note that hyperthreading does consume more power, so is considered less efficient in that respect.)

About a year ago I shutoff HT on a PC to see if it would run a process more quickly, and it did. So no, they didn't "lick" HT slowdowns "a few years ago."

Quote

Edit: Also, your results with Handbrake are way off. Based upon what you've revealed thus far, I suspect that you've got hard drive problems.

See above. No, it's not HD problems.

Quote

'Seems that you need some traditional troubleshooting. What app are you having trouble with?

I'm having issues with the android SDK. For older platforms and smaller screens, it runs reasonably. But for larger screens and newer systems, its nearly unusable. I'm using the Atom CPU setup, with the lastest patch for 10.8.2 (even though I'm in 10.7... seems to be an issue in 10.7.5 too.) I was trying to use snapshots to avoid boot time, but then I had to turn off GPU acceleration. Seems like I'm better with that on since I have it on for a while. Otherwise it's verrrry sluggish.

The HD is barely being hit. I've got 10GB of RAM.

Now that I can turn off HT, I'll run some tests and see if there's any performance boost.

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With HT off, there is a difference... but only about 10%, if that.

FWIW, here's a CPU chart of the app starting. On the left is with HT off, on the right is with it on.


As far as disk access goes, it's pretty much all in the RAM when I restart the app:

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Android SDK is totally messed up on the Mac. Slow as mud.

What version of the OS are you running?

If you've got the Java Preferences in your Utilities folder, run it and drag the 32-bit version of Java over the 64-bit version. If you've got the Java pref pane, you've got 1.7 and you're hosed.