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Multiplier vs GFlops - Page 2

post #11 of 14
nooooooooo problemo
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post #12 of 14
You should be getting 26 Gflops 400 * 10, I got 25 with slower memory and using high memory setting in IBT. http://www.overclock.net/11909751-post528.html
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post #13 of 14
imo its not the multi thats doing it.
i was doing some temp testing a few days ago, as i changed my TIM.
and i was getting big differences in gflops, from 32 to 42.

you have to run ibt properly
before running, open task manager and see the amount of free ram.
for example i have 2550mb free ram so in IBT i enter a custom amount of 2500. (just below the free amount)
then i change the threads from auto to 4 (quad core)
now every run i make i always get around 40-42 gflops.

"
" I would choose 'free' memory as available memory will also make use of cache memory which must be storing data for other applications aswell. Windows may free up some physical memory from the cached memory during testing but not totally and i think the rest will be the virtual memory as a compensation.

Available = Free + (Cached - Modified)"

running just free memory will help you get higher gflops, as its just using free ram and not cached ram
this should also have 4 or 2 cores running at 100%"

this will give you more consistent gflops score, but will also make your temps higher, as more gflops, the more the cpu is stressed

full details on running IBT properly http://www.overclock.net/intel-cpus/...test-linx.html
Edited by j.col - 3/5/11 at 6:45am
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post #14 of 14
Quote:
Originally Posted by mm67 View Post
You should be getting 26 Gflops 400 * 10, I got 25 with slower memory and using high memory setting in IBT. http://www.overclock.net/11909751-post528.html
that result is not accurate as he is using the set "High" amount of ram to test.
for IBT to be accurate it has to set at custom, with your free amount of ram used for the test.

even saying that lol,
his result is actually what he should be getting for a dual core cpu @ 4.0GHz
as 4 (ghz) x 8 = 32 gflops (maximum)
he should be getting at least 75% of this, so 75% of 32 = 24 or higher gflops.

if you run custom ram. you should get the same gflops on every run.
using the standard, high or maximum tests in IBT and you can get different gflops on every run

some more info from link above

"Linpack uses 64 bit(double precision)floating point numbers to store the coefficient matrix etc.
It also uses SSE(2) instruction set & registers to run as fast as possible.Each SSE2 register is 128 bit wide,so we can pack 2 64 bit values in a single register.Current processors can perform a multiply-add operation on each 64 bit value in a single cycle.So it can do 2 multiplies+2 adds per cycle,which translates into 4 FLOP(floating point operations)per cycle.This is for one core.For a dualcore the value is 8 FLOP/cycle.With a quadcore it is 16.

Now let's calculate cpu performance in term of GIGAFLOPS for a few chips:

singlecore @ 2 GHz:2X4=8 GIGAFLOPS
Dualcore @ 3 GHz:3X8=24 GIGAFLOPS
quadcore @ 4 GHz:4X16=64 GIGAFLOPS
sixcore @ 4 GHz:4X24=96 GIGAFLOPS

Note that the above values are only the upper limits.The actual value we get in LinPack is somewhat lower due to the os overhead,LinPack bookkeeping & because Linpack cannot keep the CPU execution units busy all the time.


Calculating & estimating CPU performance in term of GIGAFLOPS

NOTE:From now on I use win64 with 4 gigs of ram in all the following discussion unless noted otherwise.

The gigflops value as reported by LinPack is roughly constant for a given CPU at a given core clock.The impact of ram speed & FSB is very small.
This is very important.It means we can have a fairly accurate estimate of the GIGAFLOPS we should achieve even before running the stress test.This is the index I have been talking about.
For example the index for E5200 @ 3 GHz is roughly 20 GIGAFLOPS.The ram speed & FSB could make this value change from 19 to 20.5;Hence if we run LinX/IBT and only get 15 GIGAFLOPS then we are obviously performing an improper test that is not very useful.I have seen people running an E5200 or E6300 @ 4+ GHz and only getting 13 GIGAFLOPS!!That's also why you sometimes see people getting ridculously low temps while running LinX/IBT.The temp differnce between a proper & improper run of the test could be more than 20 c°.

Furthermore,we only need one GIGAFLOPS estimate per chip.We can calculate other values by proportion.Let's say for an E8400 @ 3GHz the index is 21 GIGAFLOPS.Then for a 4GHz oc we can expect a performance value of 21X4/3=28.

But all these need to be verified.To this end,I performed a number of tests on my sig rig in vista64.First I overclocked my cpu to 3 GHz(333X9)with my ram clocked at 1066 mhz.After several runs of LinX(just to make sure) I found the GIGAFLOPS for this oc.Then I kept FSB & ram speed constant & raised the multi.In each step,I report the actual GIGAFLOPS as displayed by LinX and a value that I have calculated from the base(3GHz) oc.Here are the results:


CPU clock--------FSBXMulti---RAM Speed----Actual GIGAFLOPS---Calculated GIGAFLOPS
(GHz)--------------(MHz)
__________________________________________________ _________________
3.00--------------333X9.0---------1066--------------20.3-------------------- 20.3
3.16--------------333X9.5---------1066--------------21.2-------------------- 21.4
3.33--------------333X10----------1066--------------22.2-------------------- 22.6
3.50--------------333X10.5--------1066--------------23.1-------------------- 23.7
3.66--------------333X11----------1066--------------24.0-------------------- 24.8

As you see,the calculated & actual values are very close,which proves our point.
Also note that the calculated values are higher than actual values & the delta becomes more as we oc higher.The reason is we oc the cpu(and L1 & L2 caches),but keep the memory clock constant.To see if this is really the case I ran another test:

CPU clock-----FSBXMulti-----RAM Speed---------Actual GIGAFLOPS
(GHz)-----------(MHz)
_________________________________________________
3.00----------333X9.0----1066 with optimized settings-----20.3

3.00----------333X9.0----800 with stock settings-------------19.5


Once more our point is proven.In short,the impact of ram speed is small.The calculated value could roughly overestimate the actual value by 1%-3%.

Next let's try to make the calculated & actual GIGAFLOPS equal!This is done by overclocking CPU/FSB/RAM at the same time and by the same amount.The aim is to verify our assumption!

We start by setting CPU/FSB/RAM @ 2.5/200/800.Then we oc by 20% which is CPU/FSB/RAM @ 3/240/960.Finally we oc by 33% with CPU/FSB/RAM @ 3.33/266/1064


CPU clock--------FSBXMulti---RAM Speed----Actual GIGAFLOPS---Calculated GIGAFLOPS
(GHz)--------------(MHz)
__________________________________________________ _________________
2.50-------------200X12.5----------800--------------16.24-------------------- 16.24
3.00-------------240X12.5----------960--------------19.54-------------------- 19.49
3.33-------------266X12.5---------1064--------------21.71-------------------- 21.60

The results speak for themself.

Now let's guess the expected GIGAFLOPS for my CPU @ 4 GHz:20.3X4/3=27.06
But because I'm not overclocking my ram the actual value is a bit less.by consulting the first table I estimate the actual value to be 25.8 GIGAFLOPS.

We don't even need to find out our actual base GIGAFLOPS ourselves;We can ask others.Let's say you have an E8400.You ask other(reliable)people for an estimated(or measured) GIGAFLOPS for your chip @ stock.You are given a value of 21 GIGAFLOPS.Now you want to calculate the expected value for an oc of 3.6GHz.SO 21X3.6/3=25.2.Now a good estimate for your oc should be around 24.5 GIGAFLOPS.

The following is the estimated GIGAFLOPS for a few chips:

E5200 @ 3 GHz 19-20 GIGAFLOPS
E8400 @ 3 GHz 21-22 GIGAFLOPS
E9550 @ 4 GHz 54-56 GIGAFLOPS

I5 quadcore @ 4 GHz 59-61 GIGAFLOPS
I7 quadcore @ 4 GHz 60-62 GIGAFLOPS
Gulftown 6core @ 4 GHz 90-93 GIGAFLOPS"
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