CPU Queue vs CPU % Busy

grob115 · 12-29-2010, 11:17 AM

Am wondering if looking at the CPU process queues, vs CPU% busy, are a better indication of whether an upgrade is needed.

Afterall, processes can still queue up to be processed even if "top" doesn't shown CPU 100%. Say if it's indicating 50% busy within the top output, it's only saying that 5 out of 10 times sampled, the CPU was busy. But a process may arrive to be processed at any time, and if it arrives just when the CPU is processing something it needs to wait in the queue. Am I making senses?

Any guidelines of how many processes queued up would suggest an upgrade is required of the CPU? I've read online (believe it's Microsoft) that 2 is the figure.

paulsm4 · 12-29-2010, 01:31 PM

Hi -

You're correct - both CPU utilization (% CPU) and runlength queue (e.g. from "uptime" or "top") are both extremely useful measures.

And you're also correct that, in general, "two's a crowd" (from basic queueing theory, not just Microsoft

).

But there are no easy answers. You need to benchmark your system, determine if you're CPU bound (often the case with high %CPU), memory bound or I/O bound (high runlength queue often indicates either/both) and take appropriate steps.

In general, purchasing more RAM is often the first hardware you'd upgrade; purchasing more/better CPUs is often the last hardware you'd upgrade. But always:

a) establish a reliable baseline,
b) determine the specific problem(s), and
c) try to determine the root cause first.

IMHO ...

ilvista · 12-29-2010, 01:40 PM

i think that you can't tell if your system needs an upgrade based on the cpu utilisation.
and try to install ATOP it's way better than top

Code:

ATOP - benchabane               2010/12/29  20:39:09               10 seconds elapsed
PRC | sys   8.27s | user   6.34s | #proc    203 | #zombie    1 | #exit      9 |
CPU | sys     82% | user     64% | irq       1% | idle     54% | wait      0% |
cpu | sys     42% | user     33% | irq       0% | idle     26% | cpu001 w  0% |
cpu | sys     40% | user     31% | irq       1% | idle     28% | cpu000 w  0% |
CPL | avg1   2.18 | avg5    4.75 | avg15   8.05 | csw    10620 | intr    5108 |
MEM | tot    2.8G | free   56.9M | cache   1.9G | buff   45.8M | slab   82.4M |
SWP | tot    3.9G | free    3.9G |              | vmcom   2.1G | vmlim   5.3G |
DSK |         sda | busy      0% | read       1 | write     87 | avio    0 ms |
NET | transport   | tcpi    1469 | tcpo    1719 | udpi     238 | udpo     249 |
NET | network     | ipi     1721 | ipo     2282 | ipfrw      0 | deliv   1707 |
NET | eth0     1% | pcki    1749 | pcko    2282 | si  139 Kbps | so 1906 Kbps |