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

How did you profile your code? Not all profiling methods are equal and some find hotspots better than others. Are you loading lots of files? If so, disk fragmentation and seek time might come into play.

Maybe even sticking basic timing information into the code, writing out to a log file and examining the files on cold/warm start will help identify where the app is spending time.

Without more information, I would lean towards filesystem/disk cache as the likely difference between the two environments. If that’s the case, then you either need to spend less time loading files upfront, or find faster ways to load files.

Example: if you are loading lots of binary data files, speed up loading by combining them into a single file, then do a slerp of the whole file into memory in one read and parse their contents. Less disk seeks and time spend reading off of disk. Again, maybe that doesn’t apply.

I don’t know offhand of any tools to clear the disk/filesystem cache, but you could write a quick application to read a bunch of unrelated files off of disk to cause the filesystem/disk cache to be loaded with different info.