Saturday, 30 June 2012

The Heat is on

How do you tell what a system is doing? Or, what tool do you turn
to to see what is going on or slowing down your system?

Most people probably turn to "ps" or "top". Most people (who
use the tools) understand most of the data displayed, but probably
not all.

I have created "proc" - a top-like tool to show lots of graphs and
key data from a Linux system. Dtrace can expose tons more data
(if you know where to probe).

But, paradoxically, the more data you can see, the more rarely you
actually use the tools. ("proc" provides views of data from the
/proc filesystem - this filesystem contains huge amounts of interesting

Q: What is the one "true" data point?

A: Heat (temperature)

When I look at my iMac (I use the excellent iStat tool, which puts
little temperature graphs on the menu bar) - its the temperature which
tells me everything. High temperature means the system is busy.

Strangely, although Linux has a lot of measurements, there is nothing
which corresponds to the CPU temperature (so far, as I have found).
I have used lm_sensors and psensor and a bunch of other tools, but there
is no CPU temperature (there probably is, but I havent found it, and
its not easy to find it either).

Heat == Power. Power == $$$. So, more heat, more $$$ (watts) being
expended. And that is a very good average of what your system is doing.
(All the other stats simply provide fine grained data on subsystems,
whether CPU, Graphics, HD, or other motherboard sensors).

In looking at the 27" iMacs - they are rated at ~360W of power. That
is a lot. That includes the screen, GPU and CPU. Most of the time,
many Macs are going to be idle. (My iMac hits 90+C during heavy
duty operations, such as media encoding). I hear lots of reports
of "hot" iMacs as being normal. In fact, the Macs (and my laptop i7
CPU) are rated for up to 100C operation; at 110C, they will shut themselves

Thats a *lot* of heat.

Strangely, one cannot tune a system based on heat. When I use my
laptop, and its heavily compiling or number crunching, it gets hot.
The fan speeds up, and it gets noisy. I may pause the operation - I hate
to think what my laptop would be like if I allowed it to max out for
very long periods of time.

Wouldnt it be nice if you could get a Watts or $$$ figure out of "ps"?

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