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SubjectRe: [PATCH] HZ change for ix86
On Tue, 5 Jan 1999, Kurt Garloff wrote:

> Hey guys,
>
> lately, I've seen a couple of questions about changing HZ in the kernel for
> ix86. Your scheduler will run more often and your system might feel snappier
> when increasing HZ, that's why we want it. Overhead for doing so got
> relativlely low with recent CPUs, so me might really want it.
...
> I created a patch which changes the values of HZ to 400 and fixed all places
> I could spot which report the jiffies value to userspace. I think I caught
> all of them. Note that 400 is a nice value, because we have to divide the
> values by 4 then, which the gcc optimizes to shift operations, which can be
> done in one or two cycles each and even parallelized on modern CPUs. Integer
> divisions are slow on the ix86 (~20 cycles) and the sys_times() needs four of

I don't know anything about it (and my box is an Alpha for which HZ is
1024), but, one ignorant proposal: would it perhaps be worthwhile to have
the HZ value higher for faster (x86) systems based on the target picked in
make config? Say, your 400 for Pentium+ and 100 for 486 or lower..?

cheers,
-bp
--
B. James Phillippe . bryan@terran.org
Linux Engineer/Admin . http://www.terran.org/~bryan
Member since 1.1.59 . finger:bryan@earth.terran.org


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