by Administrator
29. June 2009 22:05
As Linux boots, you get a message that says
Calibrating delay loop... 4997.12
BogoMIPS (lpj=2498560), with some
number before the word BogoMIPS. BogoMIPS
is one of those words that confounds new Linux
users, but it’s just jargon with a simple meaning.
BogoMIPS is Linus’s invention (yes, the same
Linus Torvalds who started Linux), and it means
bogus MIPS. As you may know, MIPS is
an acronym for millions of instructions per
second — a measure of how fast your computer
runs programs. Unfortunately, MIPS isn’t
a very good measure of performance; the MIPS
measurements of different types of computers
are difficult to compare accurately. BogoMIPS
is basically a way to measure the computer’s
speed that’s independent of the exact processor
type. Linux uses the BogoMIPS number to
calibrate a delay loop, in which the computer
keeps running some useless instructions until
a specified amount of time passes. Of course,
the reason for killing valuable processor time
like this is to wait for some slowpoke device to
get ready for work.
Oh . . . about LPJ — it’s a recent term that
stands for loops per jiffy, and it’s another measure
of time delay used by the kernel. The Linux
kernel considers time in increments of jiffies,
and a jiffy is defined as the time period that is
equal to one second divided by the value of a
kernel variable named HZ. In other words, there
are HZ jiffies in each second.
77c75d2d-19ec-449f-bfae-ab6f4ea29b7b|0|.0
Tags: linux