Re: Increasing HZ (patch for HZ > 1000)

Pavel Machek
2003-12-12T22:10:22Z

Hi!

> Just one more thing about the patch I sent. I think it addresses
> something unclean in the bogomips computation. For example, in
> arch/i386/kernel/cpu/proc.c, you have:
>
> seq_printf(m, "\nbogomips\t: %lu.%02lu\n\n",
> c->loops_per_jiffy/(500000/HZ),
> (c->loops_per_jiffy/(5000/HZ)) % 100);
>
> It's clear that for any case where 5000/HZ is not an integer, the
> bogomips decimals will be wrong and if 500000/HZ isn't an integer, the
> bogomips integer part will be wrong.
>
> For example on a 2 GHz processor with a 4000 bogomips value and HZ=1200,
> the code above will produce 3996.66 instead of 4000. Of course, as soon
> as HZ goes above 5000, you have a divide by zero right at compile time.

Well, on i386 we only run with HZ=100 and HZ=1000, so bug is latent,
but if you can find nice way to rewrite it without the bug, it would
probably be worth fixing.
Pavel

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