The Pentium D is dead

Pentium D Voltage Mod
Pentium D Voltage Mod (Photo credit: DandyDanny)

Just as they faced up to the inevitability that they could no longer keep producing ever faster processors, Intel released the “Pentium D” – a dual Pentium CPU.

The two Pentiums were not on the same die though and the whole thing gobbled energy, heated quickly and generally performed pretty poorly in comparison to the following on generation of two-CPUs-on-the-same-piece-of-silicon.

In 2005, though, having found a new job after a brief post-election period of enforced idleness, I bought a Pentium D based motherboard from the now late and lamented Morgan Computers on New Oxford Street. Morgans specialised in selling cheap end of line machines and I was both happy with the performance (earlier in the year I was building machines out of Pentium 90s!) and the price.

But the heat was a perennial problem. As the box clogged up with dust, as it inevitably did, or the heatsink‘s efficiency declined, the machine would first slow (as the cores were throttled) or just peg out at a random time.

Latterly it wasn’t even lasting 10 minutes or less with X Windows running – even though I’d invested in a much bigger heatsink.

So, tonight it was dismembered – the disk being fed into a standalone mounter so I could extract what I needed, the NVidia card removed (and the RAM) and the heavy frame chucked out. I would guess it will be gone by the morning, so efficient are the metal gatherers round here.

To upgrade or not

I am writing this blog on a PC that is, essentially, seven years old. It has a Pentium D processor block – so while it has two CPUs they are on separate cores and that shows in terms of speed and power consumption.

But as a workhorse for writing documents, blogs or even compiling the odd piece of code, it does the job.

Should I replace it with something better?

Ondemand scheduling does not work on the Pentium 4

Pentium D logo as of 2006
Image via Wikipedia

Finally got to the bottom of my issue with power saving and scheduling on my Pentium D machine (essentially a dual core Pentium 4).

It seems apparently lowering heat output (the Pentium D is a notoriously hot running processor), the “ondemand” frequency scheduler is not likely to save power in the real world and has been deliberately broken by the kernel maintainers.

As an email on LKML from October 2009 put it:

p4-clockmod is NOT true CPU frequency scaling, it just forces the CPU to  idle on a periodic duty cycle and has no effect on CPU frequency. The  clock modulation feature is basically just engaging the same mechanism  the CPU uses to reduce heat output when it gets too hot, and which is  not meant as a power saving mechanism. When engaged, it does reduce heat output and power usage, but not as much as it reduces system  performance, and means the system will simply take longer to return to  idle. In short, using p4-clockmod can only increase power usage in any real workload.

Pentium D and frequency scaling: help needed

Intel Pentium D 805 Dual Core 2.66 GHz
Image via Wikipedia

This is a technical problem that has defeated me, so maybe someone could help.

My main, everyday, desktop is a bit old, but it works well now I have replaced the heatsink: it’s using a dual core Pentium D processor, with each core running at 2.67 GHz.

cat /proc/cpuinfo tells me this should support 7 levels of frequency scaling, but I cannot seem to get it to run at anything other than full tilt all the time. I am running Ubuntu 10.10:

adrian@bossclass:~$ uname -a
Linux bossclass 2.6.35-27-generic #48-Ubuntu SMP Tue Feb 22 20:25:29 UTC 2011 i686 GNU/Linux

And I have the p4_clockmod module loaded. So how I fix this and does the Pentium D even truly support frequency scaling?