DPC Latency

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DPC Latency

Postposted on Sun Dec 29, 2013 3:33 pm

Hey guys, I happened across something called DPC latency a week or two ago and got an app called DPC Latency Checker. I see other motherboards (albeit Intel) having DPC latencies ranging from something like 60+ to 180+. Here's mine and my specs are on my sig.

Image

Are my DPC latency numbers inline with other FX/MSI users out there?
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ronch
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 10:29 am

Those numbers look fine to me. DPC checker is a great tool for making sure there's nothing going on in the background and no errant software causing system lag, stuff that wouldn't always show up under process manager. From what I've seen it's usually software installed on the specific system that will affect DPC latency more than anything else.
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 11:39 am

My previous desktop suffered from severe DPC latency. (I used the same program you gave a screenshot of to troubleshoot.) I discovered my super fancy $115 PCI wireless network adapter was causing spikes to 1,000-2,000 μs about every third second. And my DVD read-only drive caused spikes of 25,000-35,000 μs about every 15-30 seconds. (Yet my DVD burner drive of the same brand purchased at the same time was fine.) I disabled the DVD read-only drive in the device manager permanently and used wired internet whenever possible, disabling the wireless adapter in the device manager.

My current laptop has some DPC latency issues as well. (Dell from 2009, got it second hand.) Latency from 120-400 μs. Sometimes it hiccups streaming music, but disabling the wireless helps. It's minor enough that I don't notice it much when I'm Netflixing with it.

DPC latency sucks. But you have the right tool to identify it. And if you run into trouble, try disabling stuff in the device manager to see if it goes away. It's almost always from poorly written drivers, almost always from networking gear.

I wouldn't worry about less than 150 μs, though. Not that 20 μs wouldn't be better, but I don't think you're going to notice any issues with things lower than 200 μs.

12-18 months ago, I asked Scott on the podcast why there isn't any indication of DPC latency in product reviews. And his answer was that nobody seems to ever have it any more, like it was a disease from the past that was cured ten years ago. Maybe he's right. I haven't tested on my Ivy Bridge i5 build that I made a year ago, but I haven't felt compelled to since I haven't had any streaming issues with it.
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 11:46 am

Here's a screenshot from my work machine taken just now. I think this is just fine.

(Also, I'm quite content with the speed and price of my new work machine. :) )

Image
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 1:35 pm

Ran this 3 times, still getting 1000us.

But apparently Windows 8 has a problem reading correct values for DPC latency from what I read after some googling. I don't ever hear crackling or audio lag while playing games, watching videos, or listening to music.

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Re: DPC Latency

Postposted on Mon Dec 30, 2013 1:45 pm

Prestige Worldwide wrote:Ran this 3 times, still getting 1000us.


I don't have heaps of experience, but Scott's opinion seems to be that modern computers don't suffer from this nearly as much.

I also don't have experience with it in Windows 8. Does that mean the DPC Latency Checker is giving wrong readings in Windows 8? Or do the posts you found suggest that Windows 8 is actually subject to higher latency?

You won't notice it as a crackle, but like a quick dropout in streaming. Think of it like a CD that skips briefly then continues playing, except it's not a CD, it's your media player. I would describe it as a hiccup in streaming, often a half second pause like it is almost but not quite able to buffer quickly enough. I think it's also subjective not just to how bad the delay is, but how intensive the streaming requirements are in terms of bitrate. For example, I don't have trouble streaming 720p video from my laptop to my TV over HDMI, but I do at 1080p. I see occasional jerkiness in the framerate that irritates me beyond reason, yet my movie guests don't notice at all. :)

As I mentioned above, and as the Thesycon people suggest, start turning off stuff in your device manager (temporarily) to see if that brings your latency down. Sure, disabling your networking capabilities (for example) isn't a long-term fix, but at least then you know what is causing it. And then you can consider purchasing a different brand network adapter if it is bad enough.
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 2:54 pm

Windows 8 changed the way this was monitored and it is not reported correctly in DPC latency utility.

Source: http://www.thesycon.de/eng/latency_check.shtml

TheSyCon wrote:Windows 8 Compatibility: The DPC latency utility runs on Windows 8 but does not show correct values. The output suggests that the Windows 8 kernel performs badly and introduces a constant latency of one millisecond which is not the case in practice. DPCs in the Windows 8 kernel behave identical to Windows 7. The utility produces incorrect results because the implementation of kernel timers has changed in Windows 8 which causes a side effect with the measuring algorithm used by the utility. Thesycon is working on a new version of the DPC latency utility and will make it available on this site as soon as it is finished.
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 3:00 pm

Prestige Worldwide wrote:Windows 8 changed the way this was monitored and it is not reported correctly in DPC latency utility.



Thanks! :)
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Re: DPC Latency

Postposted on Mon Dec 30, 2013 3:11 pm

I have one Windows PC, but while I don't use it for recording, it does seem to report the DPC latency as expected and it's 8.1 (instead of 8) - so I wonder if this is fixed now, it mostly stays around 250us but when I do something like start and stop audio, it cracks up a bit higher.
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Re: DPC Latency

Postposted on Tue Dec 31, 2013 5:05 am

When writing to a Kingston flash drive and running uTorrent in the background, I got this.

Image

Notice the huge spike, bringing the worst-case DPC to 424ms. Before I took this there was another run (also during the flash drive write operation) and there were something like 3-4 spikes bringing up the DPC to 500+ ms. Is this to be expected?

Edit - Oh, here's another one. Also when writing to the same USB flash drive and running uTorrent.

Image

Take note, I'm using an FX-8350, which has 8 cores and a simple USB write operation along with uTorrent shouldn't be able to bog it down. If anything, one core is way more than enough to focus on writing to the USB and run uT. I say this because I've noticed that there are certain scenarios where in the system would hiccup. For example, when playing a game that is far from stressing more than a few cores, and then some hard disk read or write operation happens, the game would somehow skip a frame or two. One could definitely feel the hiccup in the system. Does a hard drive write operation bog a system down? And having multiple cores should let a CPU run many things at once without having to worry about DPC, right? Correct me on this one if I'm wrong.
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Re: DPC Latency

Postposted on Thu Jan 02, 2014 12:08 am

I hope you meant micro-seconds, not milli-seconds as that is what ms is usually used for. The difference is only *1000 so... So while the latency might spike, it's still in the frame of 0.000424 seconds.
Nice tool though.
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Re: DPC Latency

Postposted on Fri Jan 03, 2014 1:41 pm

Anandtech measures DPC latency in their reviews. Worth checking out if you're intersted. Here's a group of 990FX mobos too. Seems like around 200µs is average.
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Re: DPC Latency

Postposted on Sun Feb 09, 2014 10:50 am

Just got around to testing this, and happily my X79-UD7 seems rather excellent in this regard:

Image

This is with qBittorrent running in the background and while playing music using foobar2k
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