Messages in this thread | | | Date | Wed, 17 Apr 2002 11:04:40 +0300 | From | Matti Aarnio <> | Subject | Re: Why HZ on i386 is 100 ? |
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On Wed, Apr 17, 2002 at 02:01:42AM -0400, Robert Love wrote: > On Wed, 2002-04-17 at 01:34, Linus Torvalds wrote: > > No, it also makes it much easier to convert to/from the standard UNIX time > > formats (ie "struct timeval" and "struct timespec") without any surprises, > > because a jiffy is exactly representable in both if you have a HZ value > > of 100 or 100, but not if your HZ is 1024. > > Exactly - this was my issue. So what _was_ the rationale behind Alpha > picking 1024 (and others following)? More importantly, can we change to > 1000?
Alpha processors don't have full division hardware, they have to iterate it one bit at the time. They do have a flash multiplier, and a barrel-shifter. Shifts take one pipeline cycle, like to addition and substraction. Multiply takes 6-12 depending on model, but division takes 64...
Converting the tick to gettimeofday() seconds is faster when the tick is power of two.
> Robert Love
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