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Re: powernowd and friends

Behdad Esfahbod wrote:

The logical conclusion is that, modulating CPU speed *on demand* means nothing. No matter what speed you *think* your CPU is working on, your CPU is smart enough to consume enough power to complete the job.

My conclusion is that, CPU speed modulation on demand is as wrong as turning lights off when in blackout, and turn on again when you are back.

I know absolutely nothing about Intel processors, but here are my observations of my 1GHz Athlon4 processor in my Sony Vaio FXA-36.

Running older kernels without ACPI, temperatures are always extremely hot, sometimes reaching 70C. Back in those days with APM kernels, I used the crude but effective lvcool program which runs HLT in otherwise idle cycles. It is a userspace process that is niced to be very low priority. ACPI kernels seem to have this effect by default, with seemingly less overhead and no longer appearing as using 100% CPU all the time like the old lvcool method. Using either lvcool or ACPI would bring temperatures within the 58-64C range.

The 10 ACPI throttle states seem to be effective in slowing down the system, but some crude measurements have showed seemingly ZERO DIFFERENCE in temperature or power usage. Thus I have ignored tweaking that interface.

Only recently did cpufreq begin working with K7 processors. Running at 500MHz I have regular operating temperatures in the 46-52C range and extended battery life. After playing with cpufreq for a day, it was too much of a hassle for me to tweak manually so I pretty much ignored it until I discovered powernowd. I like powernowd because I get the benefits of low temperatures and extended battery life, but it automatically jumps to full speed if I do processor intensive things like compiling.

The vast majority of the time however I am only using my laptop to ssh into other boxes, so I like that it automatically drops to minimum speed where my regular desktop apps are mostly idle cycles, with the exception of brief jumps when large applications are loading.

Anecdotally I do not "feel" the effects of the slower speed, probably because with powernowd default settings it has a hair-trigger to jump to maximum speed when the CPU when it is needed.

fedora.us powernowd package


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