> > > -----Ursprüngliche Nachricht-----
> > > Von: Matthew Wilcox [mailto:Matthew.Wilcox@genedata.com]
> > > Gesendet am: Dienstag, 17. August 1999 16:32
> > > An: Wichert, Gerhard
> > > Cc: linux-kernel@vger.rutgers.edu; linux-mm@kvack.org
> > > Betreff: Re: [bigmem-patch] 4GB with Linux on IA32
> > >
> > > On Mon, Aug 16, 1999 at 06:29:30PM +0200, Andrea Arcangeli wrote:
> > > > Performance degradation:
> > > >
> > > > Close to zero.
>
> So, here are some additional nubers based on this little
> worst case bench from Andrea Arcangeli.
>
> #define SIZE (700*1024*1024)
>
> main()
> {
> unsigned long start, stop;
> int i;
> char *buf = (char *)malloc(SIZE);
>
> if (!buf)
> perror("malloc");
>
> i = 0;
>
> __asm__ __volatile__ ("rdtsc" :"=a" (start)::"edx");
> for (; i < SIZE; i += 4096, buf += 4096)
> *(int *)buf = 0;
>
> __asm__ __volatile__ ("rdtsc" :"=a" (stop)::"edx");
>
> printf("ticks %ul\n", stop-start);
> }
>
> This bench shows the overhead for establishing the temporary
> kernel mapping for the bigmem page.
>
> Linux-2.3.13:
> run 1
> ticks 1313001994l
> run 2
> ticks 1310999320l
> run 3
> ticks 1309894069l
> run 4
> ticks 1313788902l
> run 5
> ticks 1308360521l
>
> Linux-2.3.13 with bigmem support:
> run 1
> ticks 1331834802l
> run 2
> ticks 1332486766l
> run 3
> ticks 1332231641l
> run 4
> ticks 1332125591l
> run 5
> ticks 1333419476l
>
> This shows that we get only approx. 2% overhead in the worst
> case. In real-world applications you won't probably see any
> performance degradation.
>
> Gerhard
>
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