A Windows XP help forum. PCbanter

If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below.

Go Back   Home » PCbanter forum » Microsoft Windows XP » Hardware and Windows XP
Site Map Home Register Authors List Search Today's Posts Mark Forums Read Web Partners

Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?



 
 
Thread Tools Display Modes
  #1  
Old May 21st 09, 07:57 AM posted to microsoft.public.windowsxp.hardware,comp.sys.ibm.pc.hardware.storage
Jason Stacy
external usenet poster
 
Posts: 25
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.

Ads
  #2  
Old May 21st 09, 08:35 AM posted to microsoft.public.windowsxp.hardware
Rod Speed
external usenet poster
 
Posts: 320
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

Jason Stacy wrote:

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz
is theoretically faster than a single core with 3.4 MHz.


Because it is in practical situations.

I am NOT talking about additional features like Pipeling and
Hyperthreading but the core fact that the power is split over two cores.


Assume the following situation: A NON-THREADED application
needs as much CPU power as possible for some computations.


Thats not the situation where a dual core processor is theoretically faster.

On a 3.4 Mhz machine it can occupied almost 99% of
the CPU power (remaining 1 % are for system services).


When I run the same application on a two core system then
it can occupy only ONE of the two cores with 1.7 MHz. Because
it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).


Am I wrong?


No, just looking at the wrong situation.


  #3  
Old May 21st 09, 08:35 AM posted to microsoft.public.windowsxp.hardware
Rod Speed
external usenet poster
 
Posts: 320
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

Jason Stacy wrote:

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz
is theoretically faster than a single core with 3.4 MHz.


Because it is in practical situations.

I am NOT talking about additional features like Pipeling and
Hyperthreading but the core fact that the power is split over two cores.


Assume the following situation: A NON-THREADED application
needs as much CPU power as possible for some computations.


Thats not the situation where a dual core processor is theoretically faster.

On a 3.4 Mhz machine it can occupied almost 99% of
the CPU power (remaining 1 % are for system services).


When I run the same application on a two core system then
it can occupy only ONE of the two cores with 1.7 MHz. Because
it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).


Am I wrong?


No, just looking at the wrong situation.


  #4  
Old May 21st 09, 08:52 AM posted to microsoft.public.windowsxp.hardware
Dalo Harkin[_14_]
external usenet poster
 
Posts: 2
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?


Its not a case of right or wrong -
A single CPU core will be faster, but only in certain circumstances
(non hyperthreading apps as you say)
But its the OS that uses the cores and not necessarily the program.

If you have a multi core CPU most of the windows tasks are being
handled between the cores, so the load is much less than a single core
CPU

You are basing your ideas on just the program and not the OS

and nearly all Core2Duo CPUs have more Cache than their single core
comparisons


--
Dalo Harkin
Posted via http://www.computerhelpforums.net

  #5  
Old May 21st 09, 08:52 AM posted to microsoft.public.windowsxp.hardware
Dalo Harkin[_14_]
external usenet poster
 
Posts: 2
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?


Its not a case of right or wrong -
A single CPU core will be faster, but only in certain circumstances
(non hyperthreading apps as you say)
But its the OS that uses the cores and not necessarily the program.

If you have a multi core CPU most of the windows tasks are being
handled between the cores, so the load is much less than a single core
CPU

You are basing your ideas on just the program and not the OS

and nearly all Core2Duo CPUs have more Cache than their single core
comparisons


--
Dalo Harkin
Posted via http://www.computerhelpforums.net

  #6  
Old May 21st 09, 11:49 AM posted to microsoft.public.windowsxp.hardware
Bob Willard
external usenet poster
 
Posts: 273
Default Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?

Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


As you've already noted, the gain in moving a workload from a
monoprocessor to a multiprocessor depends on the workload. Doh.

Some workloads will gain nothing, while some will scale almost linearly
(up to some maximum number of processors).

I do have some experience in constructing workloads to show how
wonderful multiprocessors a when one of my artificial workloads ran
on a monoprocessor, the OS reported that the app got 100% of CPU time;
when it ran on a dual-processor, the OS reported that the app (fully
decomposed by hand) got 205% of CPU time. Amazing, eh?

My father would say: "Benchmarks don't lie, but liars do benchmark".
--
Cheers, Bob
  #7  
Old May 21st 09, 11:49 AM posted to microsoft.public.windowsxp.hardware
Bob Willard
external usenet poster
 
Posts: 273
Default Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?

Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


As you've already noted, the gain in moving a workload from a
monoprocessor to a multiprocessor depends on the workload. Doh.

Some workloads will gain nothing, while some will scale almost linearly
(up to some maximum number of processors).

I do have some experience in constructing workloads to show how
wonderful multiprocessors a when one of my artificial workloads ran
on a monoprocessor, the OS reported that the app got 100% of CPU time;
when it ran on a dual-processor, the OS reported that the app (fully
decomposed by hand) got 205% of CPU time. Amazing, eh?

My father would say: "Benchmarks don't lie, but liars do benchmark".
--
Cheers, Bob
  #8  
Old May 21st 09, 04:25 PM posted to microsoft.public.windowsxp.hardware
No_Name
external usenet poster
 
Posts: 15
Default Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?

On May 21, 7:57*am, (Jason Stacy) wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


I think the real world answer may be that many applications do require
data to and from a hard drive. Any time waiting for this will slow
the process down. Thus most applications will become multi-threaded.

Also, although the processor speed may be so and GHz (nb most CPUs run
at GHz speed these days rather than MHz speed), the different levels
of cache memory are slower .

Have you done any actual tests to see which is fastest?

Michael
  #9  
Old May 21st 09, 04:25 PM posted to microsoft.public.windowsxp.hardware
No_Name
external usenet poster
 
Posts: 15
Default Should Core 2 Duo CPU not be theoretically slower than singlecore with double MHz?

On May 21, 7:57*am, (Jason Stacy) wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


I think the real world answer may be that many applications do require
data to and from a hard drive. Any time waiting for this will slow
the process down. Thus most applications will become multi-threaded.

Also, although the processor speed may be so and GHz (nb most CPUs run
at GHz speed these days rather than MHz speed), the different levels
of cache memory are slower .

Have you done any actual tests to see which is fastest?

Michael
  #10  
Old May 21st 09, 09:14 PM posted to microsoft.public.windowsxp.hardware
Arno[_2_]
external usenet poster
 
Posts: 57
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

In comp.sys.ibm.pc.hardware.storage Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is
theoretically faster than a single core with 3.4 MHz. I am NOT
talking about additional features like Pipeling and Hyperthreading
but the core fact that the power is split over two cores.


Well, it depends highly on the workload. For a non-paralellizable
workload (which is surprinsingly common), the 2-core is only 50%
as fast and nothing at all can be done about it. For a very well
paralellizable workload, it benefits from two caches instead of
one.

Assume the following situation: A NON-THREADED application needs as
much CPU power as possible for some computations. On a 3.4 Mhz
machine it can occupied almost 99% of the CPU power (remaining 1 %
are for system services).


When I run the same application on a two core system then it can
occupy only ONE of the two cores with 1.7 MHz. Because it is
non-threaded it cannot request the other core as well. So it must
be slower (given all other side-conditions are equal).


Am I wrong?


No. You have it exactly right.

Arno

  #11  
Old May 21st 09, 09:14 PM posted to microsoft.public.windowsxp.hardware
Arno[_2_]
external usenet poster
 
Posts: 57
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

In comp.sys.ibm.pc.hardware.storage Jason Stacy wrote:
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is
theoretically faster than a single core with 3.4 MHz. I am NOT
talking about additional features like Pipeling and Hyperthreading
but the core fact that the power is split over two cores.


Well, it depends highly on the workload. For a non-paralellizable
workload (which is surprinsingly common), the 2-core is only 50%
as fast and nothing at all can be done about it. For a very well
paralellizable workload, it benefits from two caches instead of
one.

Assume the following situation: A NON-THREADED application needs as
much CPU power as possible for some computations. On a 3.4 Mhz
machine it can occupied almost 99% of the CPU power (remaining 1 %
are for system services).


When I run the same application on a two core system then it can
occupy only ONE of the two cores with 1.7 MHz. Because it is
non-threaded it cannot request the other core as well. So it must
be slower (given all other side-conditions are equal).


Am I wrong?


No. You have it exactly right.

Arno

  #12  
Old May 22nd 09, 03:44 AM posted to microsoft.public.windowsxp.hardware
Ian D
external usenet poster
 
Posts: 381
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?


"Jason Stacy" wrote in message
...
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically
faster
than a single core with 3.4 MHz. I am NOT talking about additional
features like
Pipeling and Hyperthreading but the core fact that the power is split over
two cores.

Assume the following situation: A NON-THREADED application needs as much
CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of
the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy
only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core
as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


The 1.7GHz Core 2 Duo running single core will be slower than
a 3.4GHz P4. On the other hand, a 2.4GHz Core 2 Duo on single
core will beat the 3.4GHz P4. It's because the Core 2 processes
more instructions per clock cycle than a P4, but the ratio is less
than 2:1.

Being multithreaded does not automatically enable an application
to use more than one core. The application must be coded to utilize
multiprocessors. Most applications are multithreaded, but few can
fully utilize more than one core. If you look in the Processes tab of
Task Manager you can see how many threads an application uses.


  #13  
Old May 22nd 09, 03:44 AM posted to microsoft.public.windowsxp.hardware
Ian D
external usenet poster
 
Posts: 381
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?


"Jason Stacy" wrote in message
...
I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically
faster
than a single core with 3.4 MHz. I am NOT talking about additional
features like
Pipeling and Hyperthreading but the core fact that the power is split over
two cores.

Assume the following situation: A NON-THREADED application needs as much
CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of
the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy
only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core
as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?

J.


The 1.7GHz Core 2 Duo running single core will be slower than
a 3.4GHz P4. On the other hand, a 2.4GHz Core 2 Duo on single
core will beat the 3.4GHz P4. It's because the Core 2 processes
more instructions per clock cycle than a P4, but the ratio is less
than 2:1.

Being multithreaded does not automatically enable an application
to use more than one core. The application must be coded to utilize
multiprocessors. Most applications are multithreaded, but few can
fully utilize more than one core. If you look in the Processes tab of
Task Manager you can see how many threads an application uses.


  #14  
Old May 22nd 09, 05:12 AM posted to microsoft.public.windowsxp.hardware
DevilsPGD[_2_]
external usenet poster
 
Posts: 2
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

In message
(Jason Stacy) was claimed to have wrote:

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?


If you're comparing a single-core processor based on the "Core 2"
architecture vs a single threaded app on a Core 2 Duo then performance
will be roughly twice as fast on the single core CPU.

However, if you're comparing a P4 based CPU vs something in the Core 2
generation, then the picture is more complicated then raw clockspeed
would indicate, but the short version is that Core 2 CPUs tend to be
anywhere from 1.2x to 2.0x more efficient then P4 based CPUs at the same
clock speed.

Lastly, even if you're using a single-threaded application, the other
core will likely have other tasks to do which would otherwise borrow a
bit of CPU away from your CPU intensive single thread.
  #15  
Old May 22nd 09, 05:12 AM posted to microsoft.public.windowsxp.hardware
DevilsPGD[_2_]
external usenet poster
 
Posts: 2
Default Should Core 2 Duo CPU not be theoretically slower than single core with double MHz?

In message
(Jason Stacy) was claimed to have wrote:

I wonder why a two-core CPU with lets say 2 * 1.7 Mhz is theoretically faster
than a single core with 3.4 MHz. I am NOT talking about additional features like
Pipeling and Hyperthreading but the core fact that the power is split over two cores.

Assume the following situation: A NON-THREADED application needs as much CPU power as possible
for some computations. On a 3.4 Mhz machine it can occupied almost 99% of the CPU power
(remaining 1 % are for system services).

When I run the same application on a two core system then it can occupy only ONE of the two cores
with 1.7 MHz. Because it is non-threaded it cannot request the other core as well.
So it must be slower (given all other side-conditions are equal).

Am I wrong?


If you're comparing a single-core processor based on the "Core 2"
architecture vs a single threaded app on a Core 2 Duo then performance
will be roughly twice as fast on the single core CPU.

However, if you're comparing a P4 based CPU vs something in the Core 2
generation, then the picture is more complicated then raw clockspeed
would indicate, but the short version is that Core 2 CPUs tend to be
anywhere from 1.2x to 2.0x more efficient then P4 based CPUs at the same
clock speed.

Lastly, even if you're using a single-threaded application, the other
core will likely have other tasks to do which would otherwise borrow a
bit of CPU away from your CPU intensive single thread.
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is Off
HTML code is Off






All times are GMT +1. The time now is 05:08 PM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 PCbanter.
The comments are property of their posters.