When running multiple instances of the same target system, in a virtual network or similar, it is likely that many of the RAM, ROM, flash, or disk pages in each system are identical to the others. Simics Accelerator adds a new page-sharing feature which takes advantage of this fact to reduce host memory consumption and increase execution performance.
When the page-sharing feature is activated, at certain trigger points Simics will examine the contents of a page, comparing it with other pages examined earlier. If an identical match is found, the page is removed and instead set to share data with the other page(s).
When many pages are shared the host memory that Simics uses will be reduced and consequently it will take longer until the memory-limit is reached. If the frequency of reaching Simics memory-limit is a factor limiting performance, execution performance will also increase. Simics can also take advantage of the fact that the page is shared by sharing the generated JIT code corresponding to a shared page. This can lead to improved performance since the JIT code only needs to be created once, but also thanks to better instruction caching when many target processors use the same JIT code.
Shared pages are always read-only, if a shared page is written to, it will automatically be un-shared and the writer will be given a private copy of the page. Consequently, page-sharing works best for pages containing only instructions or data pages which are never or rarely modified.
To activate page-sharing, use the command enable-page-sharing. This command also has a -now command argument which causes all pages to be analyzed and possibly shared directly.
To monitor how much memory that is saved due to the page-sharing feature, the system-perfmeter has a -shared switch which shows how much memory in total that has been saved, in each measurement sample. (See chapter Performance in the Simics User's Guide.)
Use disable-page-sharing to deactivate the page-sharing feature. This will not cause already shared pages to be un-shared but no more pages will be shared.