Messages in this thread | | | From | "Albert D. Cahalan" <> | Subject | Re: Why HZ on i386 is 100 ? | Date | Tue, 23 Apr 2002 18:42:35 -0400 (EDT) |
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Matti Aarnio writes: > 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...
Division by 1000 is a UMULH followed by a right shift. So maybe it costs you one cycle more than division by 1024 would. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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