Basically, confirm the discovery from http://david-grs.github.io/tls_performance_overhead_cost_linux/ on my Linux box.

§main.c

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#include "tik.h"

void f();
void g();

int main(int argc, char *argv[])
{
    size_t size = 1000*1000*1000;
    tik();
    for (size_t i = 0; i < size; ++i) {
        f();
    }
    tik();
    tik();
    for (size_t i = 0; i < size; ++i) {
        g();
    }
    tik();

    return 0;
}

§fg.c

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void f()
{
  static int x;
  x++;
}

void g()
{
  static _Thread_local int y;
  y++;
}

On my box, the cost of thread-local storage is ~2x more expensive than global storage. (Compiling requires tik.)

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$ clang -shared -O -fPIC -o libfg.so fg.c
$ clang -O main.c -lfg -L .
$ LD_LIBRARY_PATH=. ./a.out
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3.9

Inspecting the generated assembly:

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f:                                      # @f
	incl	f.x(%rip)
	retq

g:                                      # @g
	pushq	%rax
	leaq	g.y@TLSLD(%rip), %rdi
	callq	__tls_get_addr@PLT
	incl	g.y@DTPOFF(%rax)
	popq	%rax
	retq

§Reference

http://cs-fundamentals.com/c-programming/static-and-dynamic-linking-in-c.php#static-and-dynamic-linking

https://docs.oracle.com/cd/E19683-01/817-3677/chapter8-1/index.html