On 08/24/2018 01:58 PM, clipka wrote:
> Am 24.08.2018 um 15:51 schrieb William F Pokorny:
> 
>> Interesting - especially it not slowing over time. Supposing:
> 
> Why should they?
> 
> Modern CPU cooling systems dissipate heat very quickly. If POV-Ray were
> to max out the cooling system's capacity, it would show within a couple
> of seconds.
> 

I've not seen that behavior for an extended render on a machine with 
turbo boost active is the short answer.

My old i7-920 - before I over-clocked it with the turbo mode turned off 
- didn't hold the turbo boost frequency for long. I was doing long 
single image isosurface stuff at the time. Dick appears to be getting a 
3.8GHz 'core' over time and under load.

A reason I suggested the grep command is I wonder if all the cores are 
maxed out with respect to the multipliers. Are some cores in fact being 
throttled? The 3.8ghz number is a core seeing a 10x 100Mhz but you can 
get up to 12x 100MHz on a core. I don't know if thermal throttling is by 
core or by die.

I further wonder how constant the reported 3.8GHz number really is. On 
my i3 the frequency values reported in /proc/cpuinfo look to be 
relatively instantaneous. I'm not under load and those MHz values change 
dramatically every time I look. I think we'd need to monitor the 
performance over time for a full image render to be sure the 3.8GHz held.

Dick is rendering frames. Maybe there is in fact some periodicity in the 
actual performance where a frame starts with turbo boost maxed out and 
then it tails off. Maybe thermal stuff isn't an issue because he is 
rendering frames and there is a cool off period between frames.

I worked for a long time on the hardware design side of CPUs and cache 
chips and power consumption/heat generation grows exponentially with 
frequency increases. Your right, if limits kick in, it happens fast. My 
thinking is 2.8GHz is the performance Intel can guarantee under all 
loads given the manufacturing process variation and shipped cooling at 
some expected "end of life." Otherwise, they'd be claiming a better base 
performance & charging for it, or, somehow handicapping the CPUs aimed 
at lower end boxes so as not to eat into their higher end - higher 
profit - business.

Though, AMD is again a serious player, maybe they are somewhat being 
forced to eat the high end business and what we see with Dick's new i5 
is a result.

All just me pondering. I don't know anything for sure - even that. :-)

> 
> Probably. There's more chip area than if the HT circuitry were
> completely absent, so there's more area to dissipate the heat. Also, the
> components that would normally be shared between HT units won't be maxed
> out and thus create less heat. So given the same cooling system, with HT
> off the CPU will indeed inevitably run cooler. But the CPU may be
> specified at a lower TDP, in which case a weaker cooling system may be
> employed and thus resulting in the same CPU temperature.
> 
> I'm not sure whether Intel does indeed produce cores with HT circuitry
> existing yet disabled, but producing non-HT CPUs in this manner does
> make sense: You can just produce HT CPUs, and if during die testing you
> find that a CPU has defective "semi-cores" you can just blow a fuse to
> disable HT and sell it as a lower-tier CPU.
> 
> Intel has employed this strategy at least as early as the 80486 days,
> when they sold dies with functional FPUs as 80486-DX, and those with
> faulty FPUs got a fuse blown and sold as FPU-less 80486-SX. And the
> external 80487 FPUs you could buy to upgrade such systems were actually
> fully-fledged 80486-DX dies that would just take over the entire system,
> disabling the 80486-SX installed in the mainboard's CPU socket.
> 
Agree & that last bit about the 80487's being in fact 80486-DX dies I 
did not know.

> 
>> My memory not quite right on things with respect to the current
>> generation of i5s, but the more cores no threads direction at similar
>> price is good news for POV-Ray.
> 
> Please don't call it "no threads". Threads are a software thing, a means
> of utilizing multiple cores by a single application without too much
> overhead. The hardware thing is "hyperthreading", a means of multiple
> execution units sharing certain functional blocks in the CPU to utilize
> them more efficiently.
> 

Good point. I got sloppy with the wording.

Bill P.

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