Performance issues following upgrade

[dlausevic]

Here is my situation fellas. My computer just died after a long period of loyal use. My power supply overloaded my board and cpu. It was a sad yet beautiful funeral.

Was running Kubuntu 6.06.2 LTS on the following hardware:

Athlon 1500+ cpu.
1gb RAM
128mb nVidia card
Onboard intel NIC
Onboard sound

Replaced the board with

Intel Core Duo 1.5ghz
VIA chipset on the mboard
2gb 667mhz RAM
Same video card
onboard NIC (don't know the type, but it works).

I fired her up and it booted up like nothing. It was slower than usual. I didn't expect anything at all, to be honest (considering my issues from years past after such a large scale upgrade).

So, now everything seems to be running slower. I was hoping to see quite an improvement in performance, but it's sluggish. At the moment, I'm burning some data dvd's to back up my data. I may just upgrade to gutsy gibbon once it's all said and done.

Is there anything I should do in the mean time to improve its performance?

Thanks guys.

[je_fro]

yeah, that's crazy dude... I thought you'd need 32bit compatability libs to boot into a linux system... that is, if you're moving from x86 to x86_64.
you're lucky she started at all in my opinion, but bwkaz will probably be along shortly to explain why it's working, albeit slowly :)

[saikee]

I expect an installed 32 bits Linux system to run on a 64 bits machine myself but not the other way round.

However while the system will run it is not optimized, especially across a different make of CPU. A re-installation should help in such case. A more up to date distro will also turn things round.

Mind you the 1.5GHz Intel CPU is not going to set things on fire. The performance will be best judged in multi-taskings where the Core Duo excels.

[JayMan8081]

You might also need to install an SMP kernel as your old CPU was not SMP compatible so Kubuntu most likely only used a single CPU kernel.

[bwkaz]

yeah, that's crazy dude... I thought you'd need 32bit compatability libs to boot into a linux system... Not if the kernel is also 32-bit. :) In that case, you can only run 32-bit binaries, since the kernel never puts the CPU into "long mode" (or whatever AMD called it), because the kernel only knows about the old 32-bit CPU info. So the CPU will still run all the old 32-bit code without any issues.

(The 32-bit compatibility libs are to run a 32-bit process under a 64-bit kernel, when the system-wide "long mode" bit has been turned on by the kernel. There's a separate bit somewhere else that controls the current effective word size, which the kernel will change per process. That's why you need 32-bit libs to run a 32-bit binary: because the kernel forces the entire process to be the same bit-width. Although actually, I'm not sure if it's the kernel that enforces this or the CPU; it's possible that the CPU would allow that "effective bit width" flag to change at any time, but changing it is really expensive. If that's the case, then you'd want to wait for a long delay (like a context switch when the scheduler picks another process to run) to change the flag. Anyway, it's one of the two that forces it.)

that is, if you're moving from x86 to x86_64. I was under the impression that the Core Duo chips didn't do 64-bit, only the Core 2 Duos? Maybe that's wrong, though; I can never keep the difference between various Intel CPUs straight.

I would suspect that the slower performance has something to do with the fact that the Intel CPU is a 1.5GHz, where your AMD was a 1500. Depending on the particular load pattern, the Intel CPUs can be a lot slower. That's especially true for the CPUs that are about a generation older, like what I believe the Core Duo is. (Mostly this was caused by the huge pipeline depth and (relatively) poor caching policy: whenever a branch got mis-predicted, lots of instructions would have to be flushed from the pipeline, and the cache missed more often, forcing more slow RAM accesses.)

However, I don't know if that's the case for sure, it'd just be my first guess. If you did get a Core 2 Duo, then that's very likely not the problem (though I didn't think the Core 2 Duos were being sold at that slow of a speed).

An SMP kernel would help (a bit: only when more than one process needs to run at the same time), but would not make your current CPU as fast as your old one. You might be able to get multithreaded programs to finish more quickly, and depending on the way various processes were spread across virtual CPUs, you might see a bit of a gain in interactivity. But it won't help a single-threaded load at all.

(Actually, the slowness may be related to hyperthreading. Have you tried with that both on and off in the BIOS?)

[dlausevic]

Thanks for the replies guys. They were indepth. First of all, the athlon chip, athlon 1500+ wasn't their 64bit chip. I moved to the initial core duo, not the core 2, so it's 32 bit still.

Anyway. I gave up, backed up all my crap and install kubuntu 7.10. Now I need to find out why my sound is disabled every other time I reboot and why magnatunes list doesn't populate on amarok anymore. If it's not one thing, it's another.

*edited to remove cuss word*