If you change the CONFIG_HZ value in a kernel (in order to obtain higher
resolution timing), do you also need to change the lpj value in the kernel
command string?
I've got a 7350 and a 3.0.4 kernel (although I've been changing CONFIG_HZ on
earlier kernels) and I've modified it from 100 to 1000. It's been working
great so far but in reading about embedded linux optimizations, the lpj value
should be measured once and then set in the kernel command string. Okay,
great. TS has always used lpj=498688 so I never messed with it even after
changing CONFIG_HZ to 1000.
Now, when I remove the lpj-498688, I get the following on the console when I
boot:
Calibrating delay loop... 98.11 BogoMIPS (lpj=49056)
Hmm...that's roughly 1/10th what it was before. So this raises some questions
given that udelay is called in thousands of places throughout the kernel and
the drivers. Is the code wasting time because lpj was set too high? If I
lower it, am I going to lose the user-space usleep resolution or break drivers?
On a related note, my goal is to improve boot times which go up significantly
when you use USB and other stuff. I managed to go from 10 seconds to just
under 6 seconds by turning off excess PTYs, statically building drivers, and
turning off kernel console output.
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