QUOTE(Ricimer @ 5.10.2009 10:00)

Each time AVP seems to be doing nothing, when stopping AV, excluding the process, pausing or disabling the performance does NOT return to normal levels. So far the only cure is to uninstall MP4. I have tracked the cause of the slowdown to the KLIF file system filter. Remove the driver from the registry and application performance returns to expected levels.
It seems that the filter driver is exceptionally slow, especially using registry access heavy applications. Until this is fixed MP4 is unusable with many applications. I'm so concerned with the performance that I've even considered not using 20 months of our 500 user license and returning to NOD32.
For now I will have to move all the test machines back to MP3, which while it does slow applications (as any AV will) they are an acceptable level.
Has anyone else experienced extreme application slowdown with MP4?
What you say rings true for me. MP4 paralyses machines that ran perfectly adequately with MP3 - especially older machines that are inevitably much slower than the latest hardware. MP4 is much more bearable on newer hardware.
I have pulled back MP4 from my network today. On one workstation, it was taking 20 seconds plus to open a new tab in Internet Explorer 8 with MP4 installed. This returned to under a second once MP3 was reinstalled.
As you say, the slow down isn't in avp.exe and it doesn't depend which options you have selected. Stopping all AV functions doesn't restore performance as you would expect. Whilst I haven't had an opportunity to test unhooking klif.sys from the registry, it would make sense for the problem to be in a low level driver such as this - I recall how problems in klif.sys have caused mayhem in the past (with one faulty MP3 update interacting with Diskeeper).
Overall, MP4 looks very good, but this issue makes it unusable for me and I'm a little sad that it wasn't picked up during testing. I'll leave it in Administration Kit ready to deploy again later on, after Kaspersky have had chance to fix this problem. As I'm intending to replace my current machines with new hardware running Windows 7, I'm going to need MP4 eventually.
Ironically, all this comes a few days after I renewed my licences for two years. Though it's OT here, that went horribly wrong, with Digital River sending me an activation code that had already been used by someone else then, when I complained, they did the same thing again! I had to call tech support to secure an emergency 30 day licence until they had had time to investigate, after which they emailed me permanent key files.