Re: ext3 performance inconsistencies, 2.4/2.6

[Linus Torvalds <torvalds@osdl.org>]

On Tue, 4 Nov 2003, Ulrich Drepper wrote:
> 
> I don't see any verison numbers mentioned.  If you want to benchmark
> NPTL use the recent code, e.g., from Fedora Core 1 or RHEL3.  Nothing
> else makes any sense since there have mean countless changes since the
> early releases.

This is actually _really_ trivial to see with a simple test program.

This is Fedora Core test3:

	#include <stdlib.h>

	/* Change this to match your CPU */
	#define NR (10*1000*1000)

	int main(int argc, char **argv)
	{
	        int i;
	        for (i = 0; i < NR; i++)
	                putchar(0);
	}

and then just time it.

I get:

	torvalds@home:~> time ./a.out > /dev/null 

	real    0m1.305s
	user    0m1.283s
	sys     0m0.004s

and

	torvalds@home:~> time LD_ASSUME_KERNEL=2.4.1 ./a.out > /dev/null 
	
	real    0m0.321s
	user    0m0.318s
	sys     0m0.003s

ie a factor of _four_ difference in the speed of "putchar()".

Interestingly, if I compile the program statically, I don't see this 
effect, and it's noticeably faster still:

	torvalds@home:~> gcc -O2 -static test.c 
	torvalds@home:~> time ./a.out > /dev/null 

	real    0m0.193s
	user    0m0.191s
	sys     0m0.002s

	torvalds@home:~> time LD_ASSUME_KERNEL=2.4.1 ./a.out > /dev/null 

	real    0m0.194s
	user    0m0.190s
	sys     0m0.004s

Is the TLS stuff done through an extra dynamically loaded indirection or
something?

		Linus