DPC Latency ckeck for your pc's

[Vicious_Angel]

A lot of people have problems with their pc's or laptops producing pop clicks and stuff.
A known issue about such behaviors is DPC latency (or deferred procedure calls latency).

A small overview of the application:
" Thesycon¢s DPC Latency Checker is a Windows tool that analyses the capabilities of a computer system to handle real-time data streams properly. It may help to find the cause for interruptions in real-time audio and video streams, also known as drop-outs. "

What is dpc latency and how our computer handles that:
Audio or video data streams transferred from or to an external device are typically handled by a kernel-mode device driver. Data processing in such device drivers is interrupt-driven. Typically, the external hardware periodically issues interrupts to request the driver to transfer the next block of data. In Windows NT based systems (Windows 2000 and better) there is a specific interrupt handling mechanism. A device driver cannot process data immediately in its interrupt routine. It has to schedule a Deferred Procedure Call (DPC) which basically is a callback routine that will be called by the operating system as soon as possible. Any data transfer performed by the device driver takes place in the context of this callback routine, named DPC for short.

The operating system maintains DPCs scheduled by device drivers in a queue. There is one DPC queue per CPU available in the system. At certain points the kernel checks the DPC queue and if no interrupt is to be processed and no DPC is currently running the first DPC will be un-queued and executed. DPC queue processing happens before the dispatcher selects a thread and assigns the CPU to it. So, a Deferred Procedure Call has a higher priority than any thread in the system.

All information taken from http://www.thesycon.de

This application has no installer, you download it and run it, also its free and a really nice tool to have to your collection.

Download the tool here

I think this post deserve a sticky for every new comer to have a clue of what their pc's can handle before blaming anything.

[Dungeon Studio]

This is really good V/A, thanks man! I hardly know anything about the guts of a PC, other than to run Defrag and clean the Registry once in a blue moon. And doing that didn't help much.

So this is good!

Sorry V/A - just reading up on it. It 'does not' point out the culprits? Just shows if big spikes are happening? I get really messed up in that Device Manager and don't know really what to look for? Interesting to see how the spikes look at least.

[Dungeon Studio]

Huh, so running it while my most CPU intense song played yielded at best a 500us spike through out it? But yet get's glitchy when it hits the VST's on the first pass through. All other consequent plays are smoother at least. So what causes that, and there's no big red spikes on this thing?

Oh yeah - and Space Bar kills the DPC App. Kinda have to finesse it around OP and all.

[Vicious_Angel]

You dont need to load orion or anything for the application to see results.
It has its own test that runs all the time and checks for latency.

This program tracks if your pc is able to handle audio and video streaming.
In our case if asio driver is stable under our system, for that we care about. This latency is produced from bad written drivers or by a device that hangs a lot of system resources and dont let the soundcard take the time it needs with the cpu.

My greek to english brain malfunction atm so i cannot give a better explanation sorry.

Run the application for about 2-3 minutes and write down your absolute maximum and where you believe you curent latency sit in the general period of those minutes.

At 500ìs you write in your post you have 0,5 sec dropout.

To have a clue my system sits somewhere at 40-60ìs and the bigest value was something like 100.

1000ìs = 1 sec.

[Vicious_Angel]

I will try to find where i discovered the hole thing (old post not on kvr tho) and if i find it i will post what latency is considered safe for our use

[Dungeon Studio]

Thanks V/A. I get what you mean, and did let it run quite a bit again. Thankfully no major spikes or anything. Just this constant low green line that goes up and down a bit, but well within the allowed region.

[Vicious_Angel]

So with a little search i found the post.

They say at full load project something like 300 is ok for our use.
A guy in this post seems to really know whats happening.

[Muse]

What do you do with the information it gives you though? It would be useful if it gave you suggestions for ways to affect or reduce the amount of DPC latency your system has

[Vicious_Angel]

Well its tricky there.
Think it like, 1 laptop has buggy wireless driver, another one has a buggy graphic card. The problem with the dpc latency is that is affected from a hell lot of different paramaters.
This tool is usefull for us to know if we have such behavior in our systems.

If we have we can move then for special optimizations of our windows.
There are a lot of usefull sites on the net for such tasks.

If you want some links i can give you some