I think dynamic linking is great for saving (DRAM) memory, but for caches I am having trouble imagining a case in which this would make a practical difference.
You would need two distinct, long-lived dynamically-linked executables, both being hot at the same time, and both having libc (or another common library) in the hotpath at the same time.
To elaborate,
- If two hot processes are the same executable, static linking would yield the same results: They will be mmap()ed to the same physical addresses (and I'm assuming physical indexing or equivalent here, otherwise ASLR really negates any dynamic linking advantage wrt caches).
- If the processes are not hot or not long-lived, everything will be dominated (by orders of magnitude) by media access, context switches, and virtual page allocation.
- Sure, we could imagine a non-hot process trashing the cache for a hot one, and doing it less so with dynamic linking. But again, context switch is the bigger concern. A complete cache flush would make little difference here.
- And I'm not even going to touch on the various cache-timing vuln mitigations out there.
That being said, I am a staunch proponent of dynamic linking being the general case, for the memory and storage savings. Security is a common argument too, and although I'm not expert enough to have an opinion on this one, I do love the traditional distro approach to packages.
You would need two distinct, long-lived dynamically-linked executables, both being hot at the same time, and both having libc (or another common library) in the hotpath at the same time.
To elaborate,
- If two hot processes are the same executable, static linking would yield the same results: They will be mmap()ed to the same physical addresses (and I'm assuming physical indexing or equivalent here, otherwise ASLR really negates any dynamic linking advantage wrt caches).
- If the processes are not hot or not long-lived, everything will be dominated (by orders of magnitude) by media access, context switches, and virtual page allocation.
- Sure, we could imagine a non-hot process trashing the cache for a hot one, and doing it less so with dynamic linking. But again, context switch is the bigger concern. A complete cache flush would make little difference here.
- And I'm not even going to touch on the various cache-timing vuln mitigations out there.
That being said, I am a staunch proponent of dynamic linking being the general case, for the memory and storage savings. Security is a common argument too, and although I'm not expert enough to have an opinion on this one, I do love the traditional distro approach to packages.