Intermittent poor performance & lagging - please help me resolve.

[omniscient]

Hi

I experience this problem intermittently (can be a couple of weeks between occurences), I've read through the "How to get the cause of High CPU usage by Apps" & "DPC/Interrupt" but I'm hoping someone else can make sense of this. Please help if you can - this problem is interfering badly with my work when it occurs, and I'm desperate to fix it.

The symptoms are;

1. Mouse, keyboard & applications lag (stop responding from a few milliseconds to a couple of seconds), the system doesn't freeze completely - e.g. process explorer will continue to refresh and update - I just simply won't be able to interact with an application.
   
2. System process using constant 25% CPU in Windows Task Manager (Processor is quad-core so I suspect the 25% is one core maxed out)
   
3. Process Explorer lists multiple "ntoskrnl.exe!KdPollBreakIn+0x1a0" in System process Threads with CPU usage constantly fluctuating between the threads but always totalling ~25%.
   
4. Xperf trace as shown in the charts below...
   

Does anyone know what the below are/mean? They appear to be the culprits to me, but this is the first time I've ever dug into a problem like this - both are Microsoft files and I can't find anything helpful searching/googling for them and the symptoms I have.

• ntkrnlmp.exe!KEAcquireSpinLockRaiseToDPC
  
• SCSIPORT.SYS - ScsiPortCompletionDpc
  

The below screenshots are the result of xperf while the symptoms were present. I eventually had to start closing applications as popups appeared saying there was not enough memory and asking me to close applications - at which point the system started to become more and more unresponsive, I feared losing my xperf trace if the system hung altogether so I started closing applications - as shown in the last chart, shortly afterwards, the symptoms disappeared and machine returned to normal operation.

CPU Sampling Summary Table

DPC CPU Usage Summary Table

I've created an overlay showing the system process, CPU Sampling & DPC CPU Usage and when applications were closed. I use mstsc.exe(Remote Desktop) and SbieCtrl.exe(Sandboxie) every day, yet this problem only occurs intermittently - so I'm sceptical to think it has anything to do with them. I started both of them immediately after I noticed the system was running correctly and the problem did not re-occur.

I will be extremely grateful for any help!

Thanks,

AJ