RE: lmbench results for 2.4 and 2.5 -- updated results

From: Nakajima, Jun (jun.nakajima@intel.com)
Date: Mon Mar 24 2003 - 15:11:52 EST


I don't think it's measuring anything useful at this point, especially with the cost of start(0) and stop(0,0) (they are eventually gettimeofday(), as far as I looked at the code) are substantial compared to page fault (sum += *end;) itself. If you move them outside the while loop, I think it's beter.

void
timeit(char *file, char *where, int size)
{
        char *end = where + size - 16*1024;
        int sum = 0;
        int n = 0, usecs = 0;

        while (end > where) {
                start(0);
                sum += *end;
                end -= 256*1024;
                usecs += stop(0,0);
                n++;
        }
        use_int(sum);
        fprintf(stderr, "Pagefaults on %s: %d usecs\n", file, usecs/n);

> -----Original Message-----
> From: Larry McVoy [mailto:lm@bitmover.com]
> Sent: Monday, March 24, 2003 12:01 PM
> To: Pallipadi, Venkatesh
> Cc: linux-kernel@vger.kernel.org; Linus Torvalds
> Subject: Re: lmbench results for 2.4 and 2.5 -- updated results
>
> On Mon, Mar 24, 2003 at 11:53:44AM -0800, Pallipadi, Venkatesh wrote:
> > --- LMbench/src/lat_pagefault.c.org Mon Mar 24 10:40:46 2003
> > +++ LMbench/src/lat_pagefault.c Mon Mar 24 10:54:34 2003
> > @@ -67,5 +67,5 @@
> > n++;
> > }
> > use_int(sum);
> > - fprintf(stderr, "Pagefaults on %s: %d usecs\n", file, usecs/n);
> > + fprintf(stderr, "Pagefaults on %s: %f usecs\n", file, (1.0 *
> > usecs) / n);
> > }
>
> It's been a long time since I've looked at this benchmark, has anyone
> stared at it and do you believe it measures anything useful? If not,
> I'll drop it from a future release. If I remember correctly what I
> was trying to do was to measure the cost of setting up the mapping
> but I might be crackin smoke.
> --
> ---
> Larry McVoy lm at bitmover.com
> http://www.bitmover.com/lm
> -
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