Messages in this thread | | | Date | Thu, 7 Jan 1999 17:38:08 +0000 (GMT) | From | Riley Williams <> | Subject | Re: [PATCH] HZ change for ix86 |
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Hi James.
>> 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 them.
> 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..?
If we were going to do this, I'd suggest 400 for Pentium+, 200 for 486 and 100 for 386 class systems as being more reasonable, and still maintaining the shift-optimisation mentioned above...
Best wishes from Riley.
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