Re: [Patch] Re: Nasty suprise with uptime

[Benjamin LaHaise <bcrl@redhat.com>]

On Thu, Nov 01, 2001 at 10:34:53AM -0500, Richard B. Johnson wrote:
> Well not exactly zealots. I test a lot of stuff. In fact, the code
> you propose:
> 
> 	if(++jiffies==0) jiffies_hi++;
> 
> ... actually works quite well:

Uhm, no, it really doesn't.  See how it pairs with other instructions and 
what the cost is when it doesn't have to be as bad:

this:
	unsigned long a, b;
	if (++a == 0) b++;
gives:
        movl    a, %eax
        movl    %esp, %ebp
        incl    %eax
        testl   %eax, %eax
        movl    %eax, a
        je      .L3
.L2:
        popl    %ebp
        ret
        .p2align 4,,7
.L3:
        incl    b
        jmp     .L2

which is really gross considering that:

	unsigned long long c;
	c++;

gives:

        addl    $1, c
        adcl    $0, c+4

which is quite excellent.

		-ben