T420 DPC Latency (NDIS)

Discussion in 'Lenovo' started by blinder, Jan 17, 2012.

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  1. blinder

    blinder Notebook Consultant

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    Hey,

    I rebuilt the T420 a couple of weeks ago - getting a lot of audio dropouts on skype and generally - it's nasty on my ears. dpc latency checker has an awful lot of red on it, and these symptoms didnt occur before the rebuild...

    LatencyMon tells me that ndis.sys and tcpip.sys are partly responsible, (I use the ethernet at work) ive disabled the wireless device and this makes no difference, so I think it's the NIC.

    Can someone who does not get these issues, AND who uses the ethernet NIC direct me to where they got their driver from please - so I can try and eliminate the issue, im not sure if I got the rebuild driver from Intel or Lenovo...

    thanks.
     
  2. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    I'm seeing a regular spike every 30 seconds on my T420s. However, I'm not convinced it is the LAN driver because I see the same thing if I connect via WiFi. Something is regularly probing the network connection whatever the type. Perhaps it is either Windows, Intel or Lenovo network management. Progressively disabling network services should reveal the culprit.

    However, this is a relatively new problem. When I checked the latency several months ago everything was in the green zone.

    John
     
  3. blinder

    blinder Notebook Consultant

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    John, also try pressing the hardware mute button while looking at dpclat, it's pretty shocking to see that whatever it's doing is either directly, or by proxy queueing that much work up in the kernel. I have a hunch it's something to do with the Lenovo tools/utils. It's a shame as I use those buttons a lot during work, I might try disabling/uninstalling those drivers and see where that gets me....

    edit - i'm just going to rebuild the machine on saturday morning I think, I'll see if I can establish the culprit that way I think.
     
  4. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    Today I rebooted my computer (I normally use hibernation and only reboot about once a week) and checked the latency. Everything was looking fine. :confused: So I hibernated and resumed. Still fine. Then, remembering your pointer to the audio system (I can confirm that the mute button causes a nasty latency spike), I remembered that yesterday I had been using WinAmp to play some music. So I started the WinAmp program. Regular spikes in dpclat's yellow then appeared and, after a couple of minutes, they moved into the red zone. I wasn't playing any music. What's intriguing is that the red spikes continued after I closed WinAmp. Perhaps WinAmp causes a service to start which then doesn't stop until a reboot, and that service is causing the spikes. Another interesting observation is that WinTV, which I started before WinAmp didn't cause any nasty spikes.

    John
     
  5. blinder

    blinder Notebook Consultant

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    It could be something to do with the conexant audio driver, see if you can replicate it and then disable the audio device, and see what you get from that. I first noticed these problems while using skype or windows media player (audio dropouts and generally not fluid audio). I've disabled the wifi device, and the problem still manifests, wifi is a common culprit, but it's not that, I can't try the the ethernet nic because im using it all day atm. Also try downloading LatencyMon and once you can replicate it, exit dpclat, and run LatencyMon and see what it finds, it goes a bit further than dpclat.
     
  6. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    LatencyMon comes up with:
    which tends to confirm the previous observation about the latency spikes occur when a network connection is active. However, this might just be the symptom, not the cause.

    John
     
  7. Colonel O'Neill

    Colonel O'Neill Notebook Deity

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    There's an HP version of the wired NIC driver floating around on Lenovo forums that's supposedly doing the trick for affected people.
     
  8. blinder

    blinder Notebook Consultant

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  9. blinder

    blinder Notebook Consultant

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    Seems to be fixed now,complete reformat & I'm using the HP NIC driver as well, no more audio dropouts during calls, and dpclat and latencymon look fine.
     
  10. John Ratsey

    John Ratsey Moderately inquisitive Super Moderator

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    And what happens when you press the mute button?

    John
     
  11. PatchySan

    PatchySan Om Noms Kit Kat

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    It's nice to see your problem is solved blinder, I've stickied this thread up on the T420 thread so other people with similar problems can look up to the solution.
     
  12. blinder

    blinder Notebook Consultant

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    You still get a nasty spike John, the Lenovo driver that talks to that piece of hardware is responsible for this, it queues a lot of work up in the Kernel every time it is pressed unfortunately.

    Lenovo are violating the Windows Driver development guidelines in a really shoddy way here - the guidelines say that queued pieces of work shouldn't take more than 100µs (if I remember rightly - it's been a while since I worked with drivers).

    edit - yes here are the guidelines: Device Driver Performance Considerations for Multimedia Platforms

    Hearst - I can't guarantee that this driver is the absolute solution, but event viewer is clean on boot, all devices work, and latency is fine (unless you press the mute button) I guess im saying ymmv really...
     
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