Windows 8's greatest weakness: DPC latency

[Audio-Purity]

I've discovered the Achilles' heel of Windows 8.

Windows 8 has very high DPC latency compared to Windows 7 SP1.

Windows 7: Service Pack 1 (64 bit)


Windows 8: Release Preview (64 bit)

As things stand, Windows 7 SP1 is much more suitable for streaming applications and has much better real-time capabilities than Windows 8.

Some info on DPC Latency: http://www.thesycon.de/deu/latency_check.shtml

DPC Latency Checker: http://www.thesycon.de/dpclat/dpclat.exe

LatencyMon: http://www.resplendence.com/latencymon

I got Windows 8 directly from Microsoft.
http://windows.microsoft.com/en-US/windows-8/iso

I use only genuine Microsoft operating systems.


I installed all the updates from Windows Update.

At first, I thought that it might be my system, a driver, or the version of Windows 8 I was using.

However, I had a friend run DPC Latency Checker on his system (Intel Core i5-2500K, running Windows 8: Consumer Preview) and his DPC latency is extremely high as well.

Anyone running Windows 8 is welcome to run DPC Latency Checker, take a screenshot and post the results.

Make sure the version of Windows & build number are clearly visible on the desktop when you take your screenshot.

Don't forget to specify if you're using the 32 bit or 64 bit version of Windows 8.

I do realize that Windows 8 is not yet a finished product.

However, every version of Windows 8 I've tried has this problem (Windows 8: Release Preview & Windows 8: Consumer Preview).

Unless Windows 8 has the same DPC latency as Windows 7 or lower, than I'm simply going to stick with Windows 7.

Side effects of high DPC latency are crackles, pops, stutter, drop-out problems, and underruns within an audio stream.

This can destroy the experience when listening to music, playing a game, or watching a movie.

I use my computer for gaming, listening to music, watching movies, and streaming audio & video.

I want the best experience possible.

And for now, that means using Windows 7 SP1.

I would classify Windows 8 as lagware.

I hope this problem gets fixed before Windows 8 reaches RTM status.

Unless it does, there's no chance I'd even consider purchasing Windows 8 or recommending it to anyone.

[ViRGE]

Any info on the hardware you're using? For a jump like that I would be looking at drivers to be honest, particularly video drivers since AMD and NV are rolling out WDDM 1.2 support, which has significant implications for how GPUs interact with the OS.

[sm625]

Well I would hope it is just an attempt to let the cpu spend more time idling. If you lower the amount of times the cpu has to process an RTC interrupt then it would increase battery life. If they did this I would assume they would make the RTC interrupt time variable so that it doesnt hurt responsiveness when the system is under load. But this is microsoft. God knows how, but they will find a way to make it use even more power and run slower.

[Gonad the Barbarian]

This also measures DPC latency and gives a few more details:
http://www.resplendence.com/latencymon

DPC latency can be affected by the HPET setting in your Bios (disabling improved mine). Also these settings can possibly affect it and Win8 may use the same ones:
http://forum.notebookreview.com/7364805-post14.html

Also, I get DPC latencies like the second pic on a Vista machine with an Nvidia video card. Disabling it in the device manager drops them down to like the first pic. On my Win7/Radeon machine my DPC latencies average around 50us.

[VirtualLarry]

Microsoft has changed the way interrupts are handled by the hardware in Win8, supposedly to be more power-efficient. All interrupts are funneled to a single interrupt to the CPU.

Edit: This just proves how MS doesn't care to make Windows 8 a "serious" OS - meaning, an OS for serious/professional users. They just want to make a pretty fisher-price block UI, dumbed-down for people to NEF on.

[BrightCandle]

Originally Posted by VirtualLarry

Microsoft has changed the way interrupts are handled by the hardware in Win8, supposedly to be more power-efficient. All interrupts are funneled to a single interrupt to the CPU.

Edit: This just proves how MS doesn't care to make Windows 8 a "serious" OS - meaning, an OS for serious/professional users. They just want to make a pretty fisher-price block UI, dumbed-down for people to NEF on.

I am all for power saving when doing it has no real impact on the user. But when it causes problems as this change inevitably will I don't want it. We need power saving features that are transparent and perform well when under load, not power saving features that make our computers broken!

[wirednuts]

windows 7 is going to hold on longer then xp did, in the business world. win8 is for us dumb consumers, simply put.

[ncstateguy87]

Originally Posted by wirednuts

windows 7 is going to hold on longer then xp did, in the business world. win8 is for us dumb consumers, simply put.

I agree, I expect another decade of win7 at many companies around the world, just like xp.

[sep]

Win8 = WinME

[power_hour]

Remember this OS was originally intended for mobile devices. Power and battery life are big issues and maybe they figured they could get away with this. They will likely patch this issue soon to address this. But I would definitely send MS an email advising them of your findings. They feel things are acceptable but your points could show them that might not be the case.

[Audio-Purity]

Originally Posted by ViRGE

Any info on the hardware you're using? For a jump like that I would be looking at drivers to be honest, particularly video drivers since AMD and NV are rolling out WDDM 1.2 support, which has significant implications for how GPUs interact with the OS.

The current DPC latency in Windows 8 is usually 1000 microseconds or higher, regardless of the hardware or drivers you're using.

"Why is DPC Latency so bad in Windows 8? I used a program DPC Latency Checker to measure. Windows 7 shows about 90u while sitting on the desktop but Windows 8 CP never shows anything lower than 1000u."

http://answers.microsoft.com/en-us/w...b-32c5951b8dbf

"On Windows 8, it reports DPC latency of 1000us (1ms) at the very lowest. It never reaches below 1000us, ever. It regularly spikes up in the 2-3ms (2,000-3,000us) range, and often spikes into the 20-30ms range during processing."

http://social.technet.microsoft.com/...2-cea920296271


The post's title says it all: DPC latency still unacceptably high in Windows 8 Release Preview

When amors1 is asked: "Are you having any video or audio issues at all?"

He replies: "Yes, sometimes audio signal is crackling."

http://answers.microsoft.com/en-us/w...9530108?page=1

Another post whose title is very telling: Latency is very bad in Windows 8 Consumer Preview.

"I also have this issue, although in my case, it causes occasional audio buffer underruns which end up as crackles, pops and stutters in the audio stream.

Updating the NIC driver helped slightly, but it still happens. I seriously hope that this is fixed for the RC (or whatever it is called).

Disabling devices doesn't help the issue either. I disabled as much as I could without killing the box but the DPC latency never goes below 1ms, which is horribly high and which explains the inability to play audio without underruns.

Oh, no wireless on my box either."

http://answers.microsoft.com/en-us/w...7-135920f22977

[notposting]

I guess my question is...did you notice a y problems playing audio. They already indicated they made some of these changes on purpose for power/battery life reasons. I don't think playing back an mp3 should require constant CPU use, so if it's working fine to your ears....

Wait, these are your first 2 posts here?!?

[Audio-Purity]

Yes, high DPC latency does cause problems for me.

It's also causing problems for a lot of other people who are using Windows 8.

Side effects of high DPC latency are crackles, pops, stutter, drop-out problems, and underruns within an audio stream.

This destroys the whole experience.

I've been reading reviews on AnandTech & other computer hardware websites for years.

I've also been building computers for myself & others for years.

I'm surprised that no hardware sites measured the DPC latency in Windows 8 & compared it to Windows 7.

So, I decided to post about it so people would be aware of the problem.

The last thing I want to see is someone pay several hundred dollars to purchase Windows 8 & take the time to install it, only to find out that it's lagware.

I'd also like to see this problem fixed before Windows 8 reaches RTM status.

The more people there are who are aware of the problem, the higher the chance that something will be done to fix the problem.

[Gonad the Barbarian]

I'm glad you're getting the info out there but unfortunately I think there's almost zero chance this gets addressed in Win8. MS has demonstrated pretty definitely that their priorities with Win8 are 1. battery life and 2. lowest common denominator consumers.

[ShintaiDK]

Windows 8 gonna be shorter lived than Windows ME.

[thewhat]

I've seen reports of higher DPC latency on another forum, but the guy didn't report any spikes, just overall higher values (in the yellow), which are by themselves not necessarily bad.

We'll see how it performs with finished drivers and all.. but I surely hope MS is working on this.

[CSMR]

Please update us on this when the final version comes out, thanks!

[Continuity28]

Originally Posted by thewhat

I've seen reports of higher DPC latency on another forum, but the guy didn't report any spikes, just overall higher values (in the yellow), which are by themselves not necessarily bad.

We'll see how it performs with finished drivers and all.. but I surely hope MS is working on this.

From first-hand experience, I assure you, it's not enjoyable.

As a measurement of latency, it's always worse the higher it is, whether it's stable or not. On Windows 7 I get an average DPC latency of 45 microseconds with periodic spikes of around 300, versus a constant ~1000 on Windows 8. It was very noticeable to me before investigating the issue, because I watch videos and play video games, which are very sensitive to latency. I could not enjoy any content because of the micro-stuttering, and no combination of driver has affected the latency for me. The only thing that helped slightly was reducing processor power saving options in the BIOS, which shouldn't be necessary, and still only reduced it from ~1000 to ~950.

[Kristijonas]

Strange, this DPC latency checker shows that I'm always at 1000us give or take 3. no spikes. No fluctuations. It's like it's set to be that way. latency didn't change even when I launched media player classic, winamp and youtube, all playing musics. Not sure if it's suppose to change anything.

I'm using Xonar Unified Drivers btw. 1.61. With C-Media panel, I think. In case someone is wondering how I managed to install these drivers: First I installed original ASUS drivers from Xonar DG ASUS website. Then I went on and installed Unified drivers WITHOUT clicking "driver cleanup" on the install. I think I had to select "invisible install" and "validity check override" or something like that on install. Unified Drivers 1.61 couldn't install without installing original ASUS drivers first. I don't remember if testmode was activated. And yes, in device manager it says the version is 1800, which is what latest Unified Drivers updates to.

[ninaholic37]

Trent Reznor uses primarily a Mac.

[JimmiG]

http://blog.cakewalk.com/windows-8-a...-applications/

According to these guys, latency is actually improved for professional audio applications. However, Metro probably won't be suited for these types of applications, which makes sense. Metro is designed for passive consumption of media rather than the creation of media.

[SimMike2]

Windows 8 isn't even released yet. From my past experience, they clean up a bunch of junk in the final release. All the beta releases suffer from odd bloat and weird stuff running in the background.

[wirednuts]

when does sp1 for win8 release?

sorry i had to say it

[StokesMSFT]

Hello, does anyone have ETW trace data proving this? I'd love to take a look at any etl files created with WPR or xperf that prove this high DPC. I'm going to do some examination on my systems at home to see as well. But really want to see if anyone that sees this problem in 3rd party tools also sees it in xperf and if so can I take a look or PM me please?

Thanks,
Jeff Stokes
Field Engineer
Microsoft

Mod note: he's legit. Welcome Jeff
-ViRGE

[Kristijonas]

Also someone please run dpc checker on win8 RTM.