Re: CVS commit: src/sys/arch

[Andrew Doran <ad%netbsd.org@localhost>]

On Mon, Mar 10, 2008 at 10:19:41PM +0000, David Laight wrote:

> On Mon, Mar 10, 2008 at 10:03:40PM +0000, Andrew Doran wrote:
> > 
> > Log Message:
> > Implement an optimized, preemption-safe asm version of tsc_get_timecount().
> > The C version needs work to be preemption safe. Cuts the clock cycles
> > for microtime() from 950 down to 300 on a Pentium D.
> 
> I'm not sure about this bit:
> 
> +       movl    $0, %edx
> +       subl    CC_CC(%edi), %eax       /* cc -= cc->cc_cc; */
> +       adcl    $0, %edx                /* if (cc < 0) cc += 0x100000000; */
> +       mull    CC_DELTA(%edi)          /* rcc = (cc * ci->ci_cc.cc_delta) */
> +       divl    CC_DENOM(%edi)          /*     / ci->ci_cc.cc_denom */
> +       addl    CC_VAL(%edi), %eax      /*     + ci->ci_cc.cc_val; */
> 
> I thought 'mull' did '%edx:%eax = %eax * mem32' so the value of %edx
> on entry is rather irrelevant.

Spot on, it's not right. I'll think of a way around it.
 
kThanks,
Andrew