Re: Intel Quad Core performance on CentOS 5.2 is slower

At Tue, 11 Nov 2008 18:21:38 GMT Jean-David Beyer <jeandavid8@xxxxxxxxxxx> wrote:


Robert Heller wrote:
At Tue, 11 Nov 2008 08:51:29 -0700 Steve Wampler <swampler@xxxxxxxx>
wrote:

viz wrote:
I installed CentOS 5.2 (kernel 2.6.18-92.1.17.el5) on this machine.
I expected the system to be faster compared to my another machine
(Intel P4 CPU 2.53 GHz, 1GB RAM) assuming it makes effective use of 4
cores.

However, the system is slow while running any application. When I
check the processor usage in the system monitor, it shows only one
core being used most of the time. Load on other cores is 1-3% during
this time.
Cat /proc/cpuinfo and count the number of cores seen by the OS. From
the above, it looks as though you've installed a single-core version of
the kernel. Traditionally, SMP (multi-core) versions of the kernel
are tagged with 'smp', as in: "2.6.9-67.0.22.ELsmp".

Note: Most (all?) common desktop applications are single-threaded, and
most would NOT benifit from being rewritten to be multi-threaded. A
multi-core / multi-processor system is a waste of effort for a *Desktop*
machine, unless the machine is making use of specialized applications
that really make use of SMP such as programs like Matlab or various other
number crunching and/or similar scientific applications.

I do not know if mine is a "desktop" or not; it is on the top of my desk.
One application I run is postgreSQL dbms. While most of its processing uses
a single processor, its logger, its memory cleanup, and such do use the
other processors, so there is a benefit to multiple cores.

It is not a 'pure' desktop: it is a desktop that is also a server. Here
having multiple cores/processors can be helpful. A 'pure' desktop would
be a machine that only runs desktop applications, such as, word processing,
an E-Mail client, and so on. Such a machine will see little or no
benifit from multiple cores/processors. As far as I am aware, putting a
Core 2 duo processor in a desktop or laptop that will only be used for
these sorts of apps, is *pure* hyp.


When I ran IBM's DB2 dbms, they ran a disk write process for each hard
drive, so that that could go in parallel with the other stuff.

Yes, again, we are talking about a server system.


The only other point of a desktop system with multiple cores / multiple
processors would be if one was running something like multiple instances
of SETI-at-home or something thing similar. OR if the desktop system is
also being used as a server of some sort (mail, file, IntraNet, DHCP,
proxy, etc.) such as for a small home [office] LAN.

Depending on what the machine is doing, you can get some benefit from more
than one core for ordinary desktop usage. Even if the user's process takes
100% of a CPU, the system and any other daemons, can run on another.

Most of the time these daemons are idle (unless the desktop is doing
extra duty as some kind of server). It is rare for a typical desktop
application to take 100% of a CPU for more than a few seconds, with a
modern processor.


I happen to run 4 BOINC processes to use up the waste processor time.

Also: the amount of RAM and the speed of the disk can have a large effect
on percieved computer speed. Often these factors are more significant
then most people realize. Throwing more cores/processors into a memory
starved system (or a system with a slow disk), will NOT make it faster.

Absolutely. That is why I put 8 GBytes in this machine. Right now down to
four due to a memory problem making an error every few days: corrected by
ECC, but I don't like it.



--
Robert Heller -- Get the Deepwoods Software FireFox Toolbar!
Deepwoods Software -- Linux Installation and Administration
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.

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