MagicAndre1981

How to get the cause of high CPU usage by DPC / Interrupt

1,451 posts in this topic

can you test this on the Windows 8 Developer edition (Run as VHD boot to avoid hassle with the partition) to verifiy that this only happens on Windows 7?

Also what are your PC specs?

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thanks for speedy reply

its an Acer Aspire 5051

windows 7 64-bit,

2Gb RAM (2x1 667Mhz),

ATi Radeon XPres 1100

120Gb HDD

Atheros AR5005G wifi adapter

what is VHD BOOT? - I was actually gunna UPGRADE to it later on (aswell as test it for this problem) - I would bet money it still same on windows 8. I would prefer to install fresh but I have so much stuff installed.

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seems ATHEROS wireless drivers just do not like Windows 7 full stop.

- I have seen and heard of this problem on other computers with Intel chipsets and other things causing the same problem. for me it seems to be a bug in windows 7.

thx exactly what i thought after all those tests... it doesnt matter if i use win7 from 2009 or win7 with all latest updates and it doesnt matter if i use atheros driver from 2009 or the latest... it is always the same behaviour in latency-monitor!

btw. is there a way to make a script or bat-file to deactivate and reactivate the wlan-card in the device-manager? it would be an acceptable workaround to have the possibility to switch it on and off directly from desktop ;)

btw2. the hardware on/off switch at the vaio only deactivates the driver... the spikes still happen when i use this switch... i have to manually deactivate the atheros in device manager... thats quite annoying

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i tried it in XP once and the problem was gone... I had to install once on another partition to use the Netgear Flash Utility to flash my router which was corrupted from many fw upgrades, i thought I would test it and indeed the problem was gone

I was told that DPC/IR process should NEVER used more than 1% CPU - is this true?

I use latency mon which can tell me which driver causes it but its stays in the green most of the time, sometimes spiking in red with DPC/IR - but pagefaults get hit hard almost instantly and it says its latencymon causing it? svchost does too when i run a youtube video... eitherway I seem to get hit hard by pagefaults when using latencymon - I check DPC/IR usage in Resource Monitor which us built into windows (like an advanced task manager) just type resource monitor into startsearch and drag it to taskbar for shortcut - sort the process's list by CPU usage and start downloading files and moving files out to usb drive and watch the DPC/IR process hit the top of the list ... this is how I monitor it and test for it on machines, ive had a couple of windows 7 laptops in past (one of which i remember had atheros wifi driver) and they were the same...

this problem is only noticeable by those 'tech' enough to realise something aint right... for me it was CPU usage in task manager was way higher than what totalled up in the processes window, thats how i found out, like i say i think its a bug in windows 7 and happens on most machines..either the users dont realise/notice or they have super powerfull CPU that can deal with it without affecting anything else (masking the problem).

Edited by snadge
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the latency should not be over 1000µs. Look if the USB and WiFi doesn't share the same IRQ.

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the latency should not be over 1000µs. Look if the USB and WiFi doesn't share the same IRQ.

how do i do that?

thanks

edit:

Highest DPC routine execution time (µs): 381

Responsible driver: ndis.sys (NDIS 6.20 driver, Microsoft Corporation)

DPC count (execution time <500 µs): 3264015

DPC count (execution time 500-999 µs): 0

DPC count (execution time 1000-1999 µs): 0

DPC count (execution time 2000-3999 µs): 0

DPC count (execution time >=4000 µs): 0

#

that was after 3 minutes of running...seems OK on there now but in RM the usage was still 5-15%

Edited by snadge
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what is VHD BOOT? - I was actually gunna UPGRADE to it later on (aswell as test it for this problem) - I would bet money it still same on windows 8. I would prefer to install fresh but I have so much stuff installed.

http://www.hanselman.com/blog/GuideToInstallingAndBootingWindows8DeveloperPreviewOffAVHDVirtualHardDisk.aspx

The values are fine. No latency over 500µs.

btw. is there a way to make a script or bat-file to deactivate and reactivate the wlan-card in the device-manager? it would be an acceptable workaround to have the possibility to switch it on and off directly from desktop ;)

use DevCon.exe ( http://support.microsoft.com/kb/311272 ) to enable disable the device.

Edited by MagicAndre1981
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great, thx andre i'll try that!

thx for all your help btw... everything (except the poor atheros) runs well now! great support here

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You're welcome. remember to create 2 Tasks (1 for enable and 1 for disable the device) to workaround the UAC prompts:

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alright... i have to find a proper way to do the disable/enable stuff with devCon first. i don't do things like this regularely so it will need some time to get into but after a first look, it seems to be fairly understandable. the main concept is the make a shortcut which starts the task (enalbe/disable) then... right? should i start a new topic for this things... i dont want to spam this important topic with OT stuff ;)

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reply to the UAC topic if you have questions about how to create tasks and run them.

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yeah thanks for the help, really much appreciated for that.

JUST WHEN I THOUGHT IT WAS GETTNG BETTER, ive done some testing and the DPC/IR CPU usage in resource monitor is still high, it seems to be erratic,

I ran Latency Mon during this test copying files FROM usb drive to DESKTOP and downloading at full speed of 1.8MB/s the DPC/IR usage in resource monitor was 30% (avg of 22%), when the file copying finished and downloading was still going on the usage dropped to 10-15% - but - in Latency Monitor it showed no problems with DPC/IR ...so whats going on? how can there be no issues when RM shows as much as 25% of CPU power devoted to DPC/IR

here is screenshot of Resource Monitor during file copying and downloading at 1.8MB/s:

screenshot6ey.jpg

here is screenshot of Resource Monitor after the file copying finished (but still downloading at 1.8MB/s)

screenshot1bm.jpg

here are results from latency mon: (1m50s)

Highest DPC routine execution time (µs): 1380

Responsible driver: ACPI.sys (ACPI

Driver for NT, Microsoft Corporation)

DPC count (execution time <500 µs): 2083392

DPC count (execution time 500-999 µs): 0

DPC count (execution time 1000-1999 µs): 56

DPC count (execution time 2000-3999 µs): 0

DPC count (execution time >=4000 µs): 0

Highest ISR routine execution time (µs): 493

Responsible driver: ataport.SYS (ATAPI

Driver Extension, Microsoft Corporation)

ISR count (execution time <250 µs): 1943269

ISR count (execution time 250-499 µs): 4

ISR count (execution time 500-999 µs): 0

ISR count (execution time 1000-1999 µs): 0

ISR count (execution time >=2000 µs): 0

Highest pagefault resolution time (µs): 22129

Hard pagefault count (total): 1270

Number of processes hit: 2

Pagefault count of hardest hit process: 928

Process with highest pagefault count: LatMon.exe (PID:

Do I have problems or not? the computer is definitely "sticky" when all this is going on

Edited by snadge
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please make a xperf trace and upload the trace.

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CONFIRMED THAT PROBLEM STILL PERSISTS IN WINDOWS 8

this is screenshot of DPC/IR using 13% of my dual-core CPU when downloading a file on Bit-Torrent at 1.6MB/s

screenhunter08oct052345.jpg

installed windows 8 fresh and using Atheros driver or MS 2011 driver is still the same.

what will the trace tell you? ive done all that before and it said that NDIS.SYS was the culprit

Edited by snadge
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you can't do anything against it. The only thing you can do is to buy a better Wifi NIC.

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