Two questions

In article , Mayayana wrote:

| If you had four cores it would not run at half the | speed. Same
two cores, same speed. Just that | the other | two cores would be
idle.

What I mean is that if you have a 4 GHz CPU with 4 cores then it's 1
GHz per core. With 2 cores it's 2 GHz per core. So it will actually
be slower to do a single-core operation on the 4 core than on the 2
core.

Uh, no. Each core is 4Ghz, that's the point. While a Quad-core 4Ghz processor may
not be as fast as a single core 16Ghz processor (due to Amdahl's Law), they're
still four different cores, each at 4Ghz.

What you're describing is called Hyperthreading, where one core is presented as
multiple CPU's, and the CPU cycles of the single core is shared between them.


--
Sandman

On 16/09/2015 21:23, PeterN wrote:
[]
Thanks, sounds like good information. Since I am doing pre-purchase
research, I will not be doing the experiments. I am thinking quad core
with about a 3.5 - 3.8 CPU. I know there are faster, but I am not yet
convinced that the additional price is worth the extra cost.

The price vs. performance goes up very steeply at the top end of the
performance range. I always try to come down one or two steps as you're
unlikely to notice the performance difference in typical use - unless
you are a games or doing a lot of very heavy video processing. Lower
clock speed may also result in lower temperatures, and hence better
system reliability.

--
Cheers,
David
Web: http://www.satsignal.eu

| What I mean is that if you have a 4 GHz CPU with
| 4 cores then it's 1 GHz per core. With 2 cores it's
| 2 GHz per core. So it will actually be slower to do
| a single-core operation on the 4 core than on the
| 2 core.
|
| All 4 cores are totally independent as for as GHz is
| concerned. Just as if they were on 4 separate chips, or
| for that matter in 4 separate boxes.
|

This is odd. On my current machine there's a dual
AMD 3.9. Windows see two cores. What you're saying
implies that I really have two CPUs, for a total of 7.8
GHz. But if I run CPUID it sees two cores, and it tells
me each is running at 1,800 MHz. (I presumed it was
determining a safe multiplier for a cool speed.)

Research online seems to indicate that you're right.
Yet I've never seen that, on my machine or others,
though I have to say I've never specifically looked into
it.

| Not if you only have two cores. I have sixteen cores and filters obviously
runs
| on all eight cores:
|
| http://jonaseklundh.se/files/photoshop_cpu.jpg
|

Very interesting. Your image seems to indicate
that it's going to the other extreme. Rather than
splitting the operation across 2 or 3 cores it's using
every core, presumably suffering time slices on
one or more of those. It would be interesting to know
how that operation compares to running on something
like dual core. Have you done much testing? Do you
find that an operation will be, say, 10 times faster on
the 16 core, or is it just a bit faster?

| The routine is a single operation that needs to go through the image
| bytes with a math operation. There just aren't two things to do at
| once.
|
| Of course there is. This is handled the same way 3D applications split up
a given
| scene and use a multiple cores, or multiple computers to render each part
and
| compose it to one frame in the end.
|

That does seem to be what your image is saying.
I'm surprised that could be done efficiently, given
the extra work to do things like calculate the extra
work where the sections meet each other and
contiguous pixels must be compared that are in
different sections.

"PeterN" wrote in message
...
On 9/15/2015 9:26 PM, Mayayana wrote:
Multiple cores can only be used for multiple
threads/processes. If you want to print while
using PS then a second core is nice. You may
also be able to do two things at once in PS.
But even that seems a stretch. If you do something
like apply a filter to a very large image, that's a
single operation. It can only run on one core. And
what else are youy going to do concurrently?

I imagine that's what Chris Cox is talking about.
PS can use the cores if you're demanding functionality
from multiple threads/processes at the same time,
but for one intensive operation, multiple cores will
be slower because each core is slower than the total.

On XP I use 2-core because I don't think XP
can optimally use more. Win7+ is probably
better, but optimization still means having uses for
those cores. Since I'm rarely doing more than two
things at once, I'd rather have two operations
running at 1800 MHz than have 4 cores running
at 900 MHz each, but with only one or two used.

If you're running clean, it's unlikely you'll see
much benefit from more cores, and Intel vs
AMD shouldn't matter. (Though specific CPU
models get different ratings.) In other words,
if you have PS applying a sharpen to a giant
image, maybe it takes 30 seconds, but what
else are you going to have PS do at the same
time that could increase efficiency? Not much.

The only scenario that makes sense to me for
more cores would be a system weighted down
with AV, malware hunters, excessive services,
etc. If you have 4 cores you might be able to
use them all with so much crap running, where
two cores might be forced to allocate time slices
to multiple processes, thus being slightly less
efficient. But aside from servers, it's hard for me
to see the benefit of a large number of cores.
It just means that each core is running slower.

You can research this yourself. Run Task Manager
and then use PS as usual. You'll probably find that
a demanding operation is using 50%, 25%, etc of
the CPU, depending on how many cores you have.
(2 cores -- max intesity is 50% of CPU. 4 cores --
max intensity is 25% of CPU. Etc.)
Is another process or another PS operation maxing
out another core? If your cores are not being used
then the increase in cores is just slowing down your
machine.



Thanks, sounds like good information. Since I am doing pre-purchase
research, I will not be doing the experiments. I am thinking quad core
with about a 3.5 - 3.8 CPU. I know there are faster, but I am not yet
convinced that the additional price is worth the extra cost.

Anytime I've built a new system, I never opted for the fastest
processor, second or third fastest is fast enough. I doubt that there
is any noticeable difference except in benchmark testing. In real world
scenarios, I doubt we would notice and performance difference between
the first, second, and third fastest processors.

I've always used AMD processors. Except for a period of time after the
original AMD Athlon processor was released, Intel has always been the
performance champion. For my use, AMD processors are just fine and are
an excellent value.

"nospam" wrote in message
...
In article , PeterN
wrote:

Multiple cores can only be used for multiple
threads/processes. If you want to print while
using PS then a second core is nice. You may
also be able to do two things at once in PS.
But even that seems a stretch. If you do something
like apply a filter to a very large image, that's a
single operation. It can only run on one core. And
what else are youy going to do concurrently?

I imagine that's what Chris Cox is talking about.
PS can use the cores if you're demanding functionality
from multiple threads/processes at the same time,
but for one intensive operation, multiple cores will
be slower because each core is slower than the total.

On XP I use 2-core because I don't think XP
can optimally use more. Win7+ is probably
better, but optimization still means having uses for
those cores. Since I'm rarely doing more than two
things at once, I'd rather have two operations
running at 1800 MHz than have 4 cores running
at 900 MHz each, but with only one or two used.

If you're running clean, it's unlikely you'll see
much benefit from more cores, and Intel vs
AMD shouldn't matter. (Though specific CPU
models get different ratings.) In other words,
if you have PS applying a sharpen to a giant
image, maybe it takes 30 seconds, but what
else are you going to have PS do at the same
time that could increase efficiency? Not much.

The only scenario that makes sense to me for
more cores would be a system weighted down
with AV, malware hunters, excessive services,
etc. If you have 4 cores you might be able to
use them all with so much crap running, where
two cores might be forced to allocate time slices
to multiple processes, thus being slightly less
efficient. But aside from servers, it's hard for me
to see the benefit of a large number of cores.
It just means that each core is running slower.

You can research this yourself. Run Task Manager
and then use PS as usual. You'll probably find that
a demanding operation is using 50%, 25%, etc of
the CPU, depending on how many cores you have.
(2 cores -- max intesity is 50% of CPU. 4 cores --
max intensity is 25% of CPU. Etc.)
Is another process or another PS operation maxing
out another core? If your cores are not being used
then the increase in cores is just slowing down your
machine.

Thanks, sounds like good information.

it's completely bogus information.

Since I am doing pre-purchase
research, I will not be doing the experiments. I am thinking quad
core
with about a 3.5 - 3.8 CPU. I know there are faster, but I am not yet
convinced that the additional price is worth the extra cost.

that's plenty fast.

what's more important is getting an ssd and a lot of memory, 16 gig
should be sufficient unless you're *really* pushing it hard.

16 gigs is a good amount of ram. If my motherboard supported 32 gigs,
I'd use it since the cost of RAM is cheap. Getting an SSD is not so
important. For example, Photoshop will launch faster when it's
installed on an SSD but the app itself won't run any faster. There's a
benefit to using an SSD as a scratch disk for Photoshop if the image
doesn't fit into RAM. If the image does fit into RAM and you've got
lots of RAM, there will be no performance benefit to having an SSD. The
cost and size of SSD vs. HDD may be enough of a factor to use HDD.

"Mayayana" wrote:
| What I mean is that if you have a 4 GHz CPU with
| 4 cores then it's 1 GHz per core. With 2 cores it's
| 2 GHz per core. So it will actually be slower to do
| a single-core operation on the 4 core than on the
| 2 core.
|
| All 4 cores are totally independent as for as GHz is
| concerned. Just as if they were on 4 separate chips, or
| for that matter in 4 separate boxes.
|

This is odd. On my current machine there's a dual
AMD 3.9. Windows see two cores. What you're saying
implies that I really have two CPUs, for a total of 7.8
GHz. But if I run CPUID it sees two cores, and it tells
me each is running at 1,800 MHz. (I presumed it was
determining a safe multiplier for a cool speed.)

That sounds like you actually have just 1 core, and it
is hyperthreaded.

Can you find something that tells what the chip actually
is? Google suggests that there are AMD dual core 3.9GHz
chips (AMD A6-6400K). But it that is running at 1.8GHz
you should be seeing effectively 4 cores. (I'm not
familiar with your software, so it might not show logical
cores, but only the real ones.)

Research online seems to indicate that you're right.
Yet I've never seen that, on my machine or others,
though I have to say I've never specifically looked into
it.

The OS, or whatever software you use to see it, doesn't
necessarily distinquish between real cores and
hyperthreaded logical cores.

And with a multi-core chip one has to be careful to
disable hyperthreading in the BIOS configuration if that
is not wanted. Otherwise a 2 core chip can show up as 4
logical cores, but instead of getting the expected extra
processing power it doesn't happen unless the load is
spread over at least 4 CPU intensive programs.

You might want to check your BIOS configuration too!

--
Floyd L. Davidson http://www.apaflo.com/
Ukpeagvik (Barrow, Alaska)

More thoughts...

From what you and Floyd have said, it seems
that one can't assume the level of core
optimization -- that it could be 0 to almost
100%, depending on the operation and the
software.

That makes me wonder about something else.
I don't know anything about bus architecture,
but I'm imagining 16 threads, each running pixel
comparisons, with each comparison needing to
be run through the CPU. Presumably there's only
one bus for those 16 cores to share, with a limit
in terms of bus speed. I wonder what, if any,
bottleneck that represents.

In article , Mayayana wrote:

| Not if you only have two cores. I have sixteen cores and filters
obviously runs | on all eight cores: | |
http://jonaseklundh.se/files/photoshop_cpu.jpg |

Very interesting. Your image seems to indicate that it's going to
the other extreme. Rather than splitting the operation across 2 or 3
cores it's using every core, presumably suffering time slices on one
or more of those. It would be interesting to know how that operation
compares to running on something like dual core. Have you done much
testing? Do you find that an operation will be, say, 10 times faster
on the 16 core, or is it just a bit faster?

More cores doesn't always end up with better performance due to what is known as
the Amdahl's Law that says that a non-unsignificant part of the CPU tasks are
sequential and cannot be parallelized.


--
Sandman

In article , PAS
wrote:

what's more important is getting an ssd and a lot of memory, 16 gig
should be sufficient unless you're *really* pushing it hard.

16 gigs is a good amount of ram. If my motherboard supported 32 gigs,
I'd use it since the cost of RAM is cheap.

32 gig is certainly nice but it's not going to make much of a
difference if you're not pushing the limits of 16 gig and most people
don't.

Getting an SSD is not so
important.

nonsense.

an ssd is one of the easiest and best ways to boost performance, and by
a *lot*, even for older computers.

For example, Photoshop will launch faster when it's
installed on an SSD but the app itself won't run any faster.

everything will be significantly faster because the majority of what
people do is i/o bound, including photoshop.

There's a
benefit to using an SSD as a scratch disk for Photoshop if the image
doesn't fit into RAM. If the image does fit into RAM and you've got
lots of RAM, there will be no performance benefit to having an SSD.

nonsense.

you've never actually tried it, have you?

The
cost and size of SSD vs. HDD may be enough of a factor to use HDD.

use both.

put the operating system and all apps on the ssd, along with any
current documents being worked on.

keep less frequently used documents on a hard drive, such as a photo
library, music library, tax returns from last year, etc.

even better, get a fusion drive (only available on macs) and let the
computer figure out what goes where based on usage patterns, all
without any effort from the user.