Re: [PATCH] stdlib: reorganize stdlib Makefile routines by functionality

["H.J. Lu" <hjl.tools@gmail.com>]

On Mon, Apr 1, 2024 at 6:13 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * abush wang:
>
> > This is test:
> > ```
> > uint64_t getnsecs() {
> >     uint32_t lo, hi;
> >     __asm__ __volatile__ (
> >         "rdtsc" : "=a"(lo), "=d"(hi)
> >     );
> >     return ((uint64_t)hi << 32) | lo;
> > }
> >
> > int main() {
> >     const int num_iterations = 1;
> >     uint64_t start, end, total_time = 0;
> >
> >     start = getnsecs();
> >     for (int i = 0; i < num_iterations; i++) {
> >         (void) lrand48();
> >     }
> >     end = getnsecs();
> >     total_time += (end - start);
> >
> >     printf("Average time for lrand48: %lu cycles\n", total_time / num_iterations);
> >     return 0;
> > }
> > ```
> > before:
> > Average time for lrand48: 21418 cycles
> >
> > after:
> > Average time for lrand48: 9892 cycles
>
> Do you see this on x86-64?  So this isn't a displacement range issue?
>
> It could be that this is a random performance change due to code
> alignment, and not actually caused by the direct call distance.
>

I have a linker patch to control section layout:

https://patchwork.sourceware.org/project/binutils/list/?series=29973

It can

1. Reduce gaps between text sections.
2. Put hot text sections close to each other.

If it can solve this issue, we should add this feature to ld.

-- 
H.J.