From owner-freebsd-net@FreeBSD.ORG  Mon Nov 12 07:10:39 2012
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Date: Sun, 11 Nov 2012 23:10:39 -0800
From: Alfred Perlstein <bright@mu.org>
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To: freebsd-net@freebsd.org, Peter Wemm <peter@wemm.org>, 
 Adrian Chadd <adrian@freebsd.org>
Subject: auto tuning tcp
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I noticed that TCBHASHSIZE does not autotune.

What do you think of the following algorithm?

Basically round down to next power of two based on nmbclusters / 64.

-Alfred

#include <stdio.h>
#include <string.h>
#include <stdlib.h>


int
main(int argc, char **argv)
{
         int nmbclusters;
         int pow2cl;

         nmbclusters = atoi(argv[1]);
         pow2cl = 1 << (fls(nmbclusters / 64)-1);
         if (pow2cl < 512)
                 pow2cl = 512;
         printf("%d\n", pow2cl);
         return (0);

}