does .so size affect virtual function performance

Question

Recently, I met a performance problem. In Vtune result, virtual function cost is always the no.1 cost, when I reduce the so size which from 48M to 37M, the performance seems better, raise up 3.9%.

I wanna know, does the .so size realy affect virtual function performance, if so, why? Thanks!

Answer 1

It is not purely size (though of course that affects paging after the program is loaded), but the number of adjustments the loader must make when loading a program. You can see that measured by setting the environment variable

LD_DEBUG=statistics

Virtual functions in particular will require a lot of adjustments during loading. For discussion on this,

• Measure time taken dynamically linking at program startup?
• Faster C++ program startups by improving runtime linking efficiency.
• Position Independent Executable (PIE) Performance

Answer 2

I use the method from the article(blogs.oracle.com/ali/entry/the_cost_of_elf_symbol) which is provided by @ErikAlapää, use RTLD_LAZY instead of RTLD_NOW when dlopen the so. However, it seems nothing help. While I compile it with less objects, it becomes better. It seems paging cache does affect the process performance.