Comparing cold-start to warm start

Question

Our application takes significantly more time to launch after a reboot (cold start) than if it was already opened once (warm start).

Most (if not all) the difference seems to come from loading DLLs, when the DLLs' are in cached memory pages they load much faster. We tried using ClearMem to simulate rebooting (since its much less time consuming than actually rebooting) and got mixed results, on some machines it seemed to simulate a reboot very consistently and in some not.

To sum up my questions are:

1. Have you experienced differences in launch time between cold and warm starts?
2. How have you delt with such differences?
3. Do you know of a way to dependably simulate a reboot?

Edit:

Clarifications for comments:

• The application is mostly native C++ with some .NET (the first .NET assembly that's loaded pays for the CLR).
• We're looking to improve load time, obviously we did our share of profiling and improved the hotspots in our code.

Something I forgot to mention was that we got some improvement by re-basing all our binaries so the loader doesn't have to do it at load time.

Answer 1

As for simulating reboots, have you considered running your app from a virtual PC? Using virtualization you can conveniently replicate a set of conditions over and over again.

I would also consider some type of profiling app to spot the bit of code causing the time lag, and then making the judgement call about how much of that code is really necessary, or if it could be achieved in a different way.

Answer 2

It would be hard to truly simulate a reboot in software. When you reboot, all devices in your machine get their reset bit asserted, which should cause all memory system-wide to be lost.

In a modern machine you've got memory and caches everywhere: there's the VM subsystem which is storing pages of memory for the program, then you've got the OS caching the contents of files in memory, then you've got the on-disk buffer of sectors on the harddrive itself. You can probably get the OS caches to be reset, but the on-disk buffer on the drive? I don't know of a way.