Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

i5 iMac and Windows 7: Headphone jack usage makes 1 core extra crazy

Hi. I wasn't even sure where to post this, but here goes...

I got a new iMac at the Apple Store a few days ago. The same day, I installed Vista Ultimate. Right away, I noticed that the cpu cores (in Task Manager) were in use, one at about 100%. The overall CPU Usage showed 35%. No apps in use.

To make a long story short, I never could figure it out.

So I went and bought Windows 7 Home Premium upgrade yesterday. Installed that (64-bit). Everything is great, but the cores were still going crazy.

Turns out that when I unplug my speakers from the headphone jack, it drops to 0% cpu usage! The performance didn't seem to have been affected by it, but it bothered me.

Any ideas what that was all about? Is that a driver issue on Apples part? I could assume it is because Apple doesn't support Win7 yet, but the driver cd contains lots of Windows 7 drivers, and it did the same thing in Vista.

Anyway, thanks.

iMac (Late 2009) i5, Mac OS X (10.6.2)

Posted on Nov 20, 2009 6:07 AM

Reply
43 replies

Nov 22, 2009 10:17 AM in response to Eric Klinger

Wow! I am having this exact same problem! I was getting ready to lose my mind trying to figure out what was cranking the cpu on my i5 and then I saw this post. Sure enough, unplugged the optical cable from the jack and cpu dropped to zero. I tried both the analog cable and the optical cable and both do the same thing. Anyone have any ideas on this? I blew away a Bootcamp Win7 install and did a full reload and then did a Bootcamp install with WinXP, same problem. Grrrrr. Thanks!

James

Nov 22, 2009 10:56 AM in response to Eric Klinger

I'm surprised to see this happening with the new iMac Core i5/i7s. I would expect Windows 7 to be better in that dept than Mac OS.

Did you manage to find and try to update audio device drivers? RealTek?

Mac OS on 2009 Mac Pro, have high cpu in audio, flash, java as well as iTunes - but not in Windows 7. If you monitor temps (Hardware Monitor for OS X, RealTemp and Everest Ultimate), you will see quick jump in temperate, which is normal, even launching windows or apps. But the Mac Pro is 20*C higher and stays there in OS X, but not Windows 7.

That whole 35%/100% would indicate thread locking going on. And more prone with Core i7 (4 cores, 8 virtual cores with hyper-threading).

The part of the older Windows kernel that had responsibility for managing scheduling was the dispatcher, and it was protected by a global lock. "The dispatcher database lock originally protected the integrity of all the scheduler-related data structures," said Kishan. "This includes things like thread priorities, ready queues, any object that you might be able to wait on, like an event, semaphore, mutex, I/O completion port timers, asynchronous procedure calls -- all of it was protected by the scheduler, which protected everything by the dispatcher lock.

/snip/
In the new kernel for Win7 and Windows Server 2008 R2, the dispatcher lock is completely gone -- a critical element of Windows architecture up until Vista, absolutely erased. Its replacement is something called fine-grained locking, with eleven types of locks for the new scheduler -- for threads, processors, timers, objects -- and rules for how locks may be obtained to avoid what engineers still call, and rightly so, deadlock. Synchronization at a global level is no longer observed, Kishan explained, so many operations are now lock-free. In its place is a kind of parallel wait path made possible by transactional semantics -- a complex way for threads, and the LPs that execute them, to be negotiated symbolically.

snip
In other words, keeping processors busy to reduce latency -- one of the methodologies that we were told years ago would help Vista -- actually reduces overall efficiency. Multicore processors work better when their logical processors (LPs) can be put to sleep, or "parked," and their active threads shipped to another LP.
Scuttling huge chunks of Vista architecture for a faster Windows

Nov 23, 2009 7:03 AM in response to Eric Klinger

Here are a few screenshots.

This is with the audio jack plugged in
This is with the audio jack unplugged

Anyway, I have not tried to look for better drivers. Yesterday I saw that there is some type of Realtek software installed, but Windows Sound Properties window says it is Cirrus Logic, so I was thinking to install SiSoft Sandra to see if it will tell me the chip maker.

@ The hatter - Interesting article. If I understand it correctly, it talked about how Vista was unable to handle more than a few cores efficiently, where in Windows 7 the unused cores will "run in place" until needed to reduce any latency of waking them up... ? Again, if I understand that correctly, wouldn't that then have changed from Vista to 7? Or at least reflected some difference.

BUT, if you look at the screenshots, core 4 and 3 are the ones that are really effected - but then what would using the audio jack cause them to go in and out of thread lock?

@ Fred Flinstone - Yes, I was able to use wireless keyboard and Magic Mouse during Windows 7 setup - but they are very problematic in Windows - especially after Apple bluetooth driver install. - So I just shut them off and use a Logitech set - I hope that gets fixes in the near future.

Nov 23, 2009 4:39 PM in response to Eric Klinger

Boy, do those screenshots look familiar! (grin) I've tried both WinXP and Win7 now and same issue with both of them in Bootcamp. One core cranks up to 100% if you plug anything into the headphone jack. This does not happen when I run OSX or run the Bootcamp partition via VMware Fusion 3.0. Fusion loads its own sound drivers for the VM which do not load support for the digital audio out so that might have something to do with it. I'm still surprised though that two different versions of Windows using two different driver versions cause the same issue. On that basis it should be relatively easy for Apple to nail this.

I did in fact call Apple on this one and they kicked me up to level two support when I mentioned that this has the "potential" to cause longevity issues with the cpu. While they don't normally support Windows they apparently did agree that they may need to look into this one asap and will be getting back to me. Keep you posted if I hear anything in the near future. For now, I just unplug my speakers when I'm in Windows so I don't keep the "oven" going. Try feeling the top of your iMac after 20 minutes of that single core on full tilt! Yikes!

Nov 25, 2009 2:42 PM in response to Eric Klinger

THANK YOU!!!!

I have been troubleshooting my new i7 iMac since it arrived last week. Could not figure it out. Did numerous clean installs of Vista, and Windows 7 in Bootcamp and the system process (acpi.sys) continued to run at 10-15% constantly.

And then I unplugged the headphone jack which I use for external speakers.

Problem solved.

Thanks again!

Nov 29, 2009 11:57 AM in response to Eric Klinger

Same issue here as well though I dont get ANY sound unless I have the external speakers plugged in.

Using taskmgr, TMonitor and HW Monitor (both from cpuid.com) with the speakers in I can see that cpu usage on Core 3 is about 40% and Core 4 is about 85%. From TMonitor all the cores are running at the downrated clock speed, around 1180Mhz, and from HWMonitor the CPU power draw is maxed at 109W.

Anyone got any ideas?

Jan 16, 2010 3:49 PM in response to Eric Klinger

I purchased a stock iMac 27" i5 yesterday and ran into this same problem. 100% CPU on the 4th core showing in processes monitor.

A little discouraged with Apple to think that something as serious as this has went without a fix or even a warning.

A fix for now...anything that will cause the core to stop going into meltdown mode. If the aforementioned placement of the plugin in the jack fixes it, do that. If it doesn't, unplug any external when using Bootcamp.

THIS WILL RUIN YOUR CPU in a fraction of its regular lifespan if you use it often in Bootcamp with the 4th core going at 100%. Processors were not meant to run like that so do whatever you have to do to keep this from happening.

Jan 17, 2010 8:19 AM in response to Eric Klinger

Adding my voice here.

Recent owner of a Core i5 iMac and new Mac user.

Exact same problem, I thought I had a virus or some spyware in Windows 7 already after a fresh install.

I have installed the HD Audio drivers from the OSX discs as recommended in another thread to fix a problem with the sound not working at all from the speakers.

So the sound works, but the CPU Usage showed consistently 35%, but for 4 cores that was actually 100% of one CPU, and moderate activity on the others. The top left of the iMac screen at the back was boiling, now it seems to cool down.

Thanks to Eric and AXW! Very slightly unplugging the jack solved the problem for now.

I understand Apple has not officially released Windows 7 BootCamp support yet, but it would be nice for them to acknowledge this problem so that we can hope to see it fixed in the Windows 7 BootCamp release.

Slightly OOT:
Out of curiosity I looked up wikipedia for the audio jack composition but I didn't get it... can someone explain what the little unplugging does?
http://en.wikipedia.org/wiki/TRSconnector#Tip.2Fring.2Fsleeveterminology

Can someone recommend a good Windows 7 widget that tracks CPU temp/usage?

Message was edited by: FabriceD

i5 iMac and Windows 7: Headphone jack usage makes 1 core extra crazy

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple ID.