Re: Patch to stop i386 longhaul from deadlocking the kernel

[Dave Jones <davej@redhat.com>]

On Thu, Nov 20, 2003 at 01:24:04PM +0000, Ashley Pittman wrote:
 > The computer is at home today but it's one of the 800Mhz boards, the fsb
 > is 133, multiplier of 60.  The speed should therefore be 798 but cpu_khz
 > is reporting it as 800.  Then it's just a case of how many bits you need
 > to remove of before 798==800.  The result is that they both need to
 > equal 768.  I've attached a user-space program which demonstrates this
 > with output.

Right, so the anding is catching the case of overflow, but neglecting
underflow. It seems to do the right thing if I change guess_fsb to do this..

    for (i=0; i<3; i++) {
        ret = _guess(speeds[i],maxmult);
        if (ret == speed)
            return speeds[i];
        if (ret < speed) {
            if ((ret+16) == speed)
                return speeds[i];
        }
    }
    return 0;
}

I need to think about this some more. I'm not entirely comfortable with
that, it looks somewhat fragile, though I can see why it works.
133 * 6 = 798
798 & ~0xf = 784
784 + 16 = 800

I wonder how well this kludge works for other frequencies.

		Dave