w_tom said:
Steve Wolfe and SIOL simply speculate why a dual processor
machine would be faster.
No. "SIOL" is only saying that at these CPU speeds nowadays, SIOL's hunger
for raw speed is satisfied long ago and he is going after responsiveness
rather than pure speed these days.
Without numbers means their reasoning
is only speculation. This machine happens to be a 486DX2-66.
It has been more responsive than many 200 Mhz Pentium
machines. Explain that? After all that is how I *feel* -
therefore it must be true!
If it works that way under XP or Linux & XWindows & KDE 3.1.4 and lets you
to hav job done without waiting for the machine, then certainly
)
Lets say we are compiling for 2 to 5 minutes. One 300 Mhz
processor ends up with most of the load of a single thread
process. Now we press a key. Keypress is a high priority
task. In a dual processor system, one processor (either one)
must stop what it is doing and respond to that higher priority
task now. Either processor will take same time to perform
that response. Response takes longer (compared to a faster
single processor system) because each dual processor is
slower. But one higher speed CPU would execute same number of
instructions to stop compiling and respond to that higher
priority task. Which is going to respond to that high
priority task quicker? Faster processor in the single CPU
system. Slower processors in a dual system simply take longer
to respond to that interrupt.
1. Ever heard of CPU affinity ? When you start new tasks, kernel gets to
decide what priority do new jobs get and whaich CPU gets to run them. It
doesn't need to be a random choice.
2. With two or more CPU setup, one CPU can get all those keypresses under
standard 18 ms interrupt while other hangs "do not disturb" sign and churns
away at the max speed.
3. When you have many tasks and many of them demand real time reaction, CPU
has to switch between tasks very frequently. Task switch costs microseconds.
When frequency of task switches rises, considerable % of CPU power goes just
for task switching. In 2.6 kernel IIRC there is setting for preferred kernel
clock for task switching. Higher clock means smoother multitasking, lower
means smaller CPU overhead.
For the bazilliont time, responsiveness is not strictly the same as speed. I
don't really care about machines response to keypress time as ling it is
under 100 ms or so. Same goes for mouse movement etc. There is some time
allowed for the operation. If operation is done during this time, machine
feels responsive, otherwise not.
It doesn't have particular sense to strive for response anything faster
than that, since user won't notice anyway, but it certainly should stay
inside some time limits...
In a dual processor system, same number of instructions must
be processed (either in CPU doing the compiling or in other
more idle CPU). But since each CPU is slower, it takes longer
to respond to that human action - a keystroke. Single
processor system using faster processor will respond faster to
interrupt of that higher priority task.
You don't seem to understand modern microprocessors. These are not the same
as microcontrollers. One instruction on the microcontroller takes small,
defined number of clocks. One instrustion on Athlon, P3, P4 etc can take
anywhere from theoretical minimum number (usually one) to several hundred
clock cycles, heavilly depending on circumstances.
CPU speed is not nearly like water in a bucket- you can't just add and
subtract it so easily.
Problem with time of response is NOT CPU speed. If it had been, even 486
would be more than enough to have responsive system- just as you have
observed before.
Problem is that CPU can't always drop what it's doing just to react to your
keypress or move a mouse pointer, open/close window etc. Sometimes it can't
because it's executign a task that just has to be done right now (like
preparing DMA transaction for CDR writing etc) and sometimes it can't
response to many requests without crapping itself just with taskswitching.
Dual CPU system can be much slower (in terms of absoulute speed- I'm not
talking about responsiveness here) or it can be much faster (more than 2x )
than uniCPU system.
UniCPU will be faster for tasks that are not multithreaded or tasks that are
neatly multithreaded so that they can be executed in in linear order or at
least in bigger chunks and cannot be executed in parallel. SInce thez tend
to use latest geenration RAMs they will excell alsso with very memory
intensive applications. Those are the situations where Duallies can't take
advantage of extra CPU and where this CPU even slows them down (cache
synchronisation- "snooping" etc)
But in situations that demand parallel execution of many threads and tasks
Duallie can be much faster, despite all.
I fnumber of tasks is not too high and L2 of both CPUs is big enough not to
get thrashed, dual CPU machine can beat single by more than 100%. Smaller
taskswitch frequency will also bring its benefits.
Steve and SIOL cannot argue with any of this because it uses
the same type of speculative reasoning that they use. IOW the
only thing we can say for certain is that Steve and SIOL
*feel* their dual processor systems are faster - without doing
a double blind test - without any numbers - and without any
good solid facts to prove their claim.
No, I "feel" my machine as more responsive. Not strictly "faster".
Just as I said, I really couldn't care less if kernel compilation takes two
or five minutes on my machine.
Or how much Gentoo's "emerge -u world" takes- as long as it is inside some
acceptable limits AND as long as I don-t see it.
Do I really need to have numbers to see for example, that on my newest
notebbok Toshiba Sattelite 5200-801 (2 GHz P4, 512 Mb DDR, GEforce 4 Go etc)
I can't watch a movie, listen to music or work under KDE smoothly when
Gentoo does its updates ?
Junk science is used to claim, for example, that a dual 300
Mhz system will be more responsive compared to a single 600
Mhz system.
But I'm not trying to be a scientist here. I was just talking about my
experiences. I don't want to invest money into making science out of this.
I had a Tualatin
[email protected] as the office machine that was meant for
tasks from office work to CD burning, printing, besides that it serves as a
firewall and router.
Now the Tualatin board is in the drawer and on its place works Dual P3-1Gig.
It works better. I can burn CDs on all three units and experience full
bandwidth under samba or ADSL and even print and never ruin writing a single
CD in the process.
What instrumentation do I need to "prove this scientifically" ?
And since neither Steve nor SIOL have included
other critical information, then we really don't know about
other essential features that more affect overall system
performance. For all we know, the motherboard in that dual
processor machine was better designed than motherboard in a
faster single processor system.
Motherboard differences can't bring or take that much from performance. But
just to keep you happy, here it goes>
Uni cpu was 1.3 GHz Tualatin, oveclocked from 100 MHz FSB to 133 MHz FSB.
Board was QDI's 10T with VIA chiopset. It had 1.5 Gb SDRAM. I have used
extra IDE card (Promise Ultra 100 Tx2) to connect four 180 Gb IDE disks
(IIRC Maxtor). Graphic card is IIRC nVidia Geforce 4 MX400.
And 3 TEACs CD-W540E units. There used to be four, but one has died recently
Oh, yes, machine has had a couple of Ethernet cards in it (i think 3), since
it also works as a firewall and router.
When I changed it to duallie, I pretty much changed only board with CPUs.
Everything else is the same. Even RAM.
Dual system runs at native speed at 133 MHz FSB.
Above is posted a fundamental theory that says Steve and
SIOL are deceiving to us.
Sure. And all that dual board sold are just a part of dirty plot to **** up
the consumer.
However unlike their junk science
reasoning, I will not claim that the above theory proves they
are wrong. I will simply say that the above theory
demonstrates their ideas can be flawed AND that we need
numbers.
But you have numbers. Just look at the benchmarks.
We are just saying that benchmarks don't cover the feeling of
responsiveness.
You have to experinece it for yourself, then decide.
If your tasks don't need it, you won't understand why people are buying this
stuff.
If your tasks need it, you won't use single CPU machine ever again.
You'll even start looking for dual CPU notebook...
I really don't care whether the dual processor system is
more responsive. I do care when junk science reasoning is
being promoted as a replacement for honesty - a claim based on
scientific principles - including numbers. They repeatedly
post a claim without numbers - or anything else to demonstrate
their claim. Lane Lewis is has quite correctly challenged
their 'facts' as only speculation based upon human perception.
So, what should I do ? All I care is performance under load that I'm
experiencing.
I don't care for standard benchmarks. 3DMarks etc don't meen crap for the
role this machine plays.
Should I mount back the Tualatin with its board and roast a couple of
hundred CD's under full load just to
"scientifically proove a point" ? No, thanks.
Why bother ? I'm not trying to sell you anything...
