Question i5 6600 disabling C-States in bios lowers boost clock? But improves performance!

AMDynamic

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Apr 23, 2016
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hi,

just a quick question everytime i use 3dmark my i5 6600 cpu boost shows as 3.86ghz during the results screen. Now i disabled all the C-states in bios and the max hits 3.56ghz??

The issue is my scores have jumped up especially in Timespy by 100 points, How comes scores across the board have gone up when boost clock has gone down? Ive not come across this before as it appears to perform better with a lesser clock speed.

thanks
 
Jun 14, 2019
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hi,

just a quick question everytime i use 3dmark my i5 6600 cpu boost shows as 3.86ghz during the results screen. Now i disabled all the C-states in bios and the max hits 3.56ghz??

The issue is my scores have jumped up especially in Timespy by 100 points, How comes scores across the board have gone up when boost clock has gone down? Ive not come across this before as it appears to perform better with a lesser clock speed.

thanks
Do you single core scores in say cpu-z increase or go down? I disable c-state on my ryzen 2600 to lock all cores to 3.7Ghz, feels faster but my single core benches go down a little bit compared the boost clock of 3.9Ghz
 

AMDynamic

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Apr 23, 2016
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I checked clocks in cpu with c states off all 4 cores seem to almost lock to 3.56 ghz

With c states on the 4 cores seem to run higher but more fluctuating 3.86 ghz then flicking to 3.60 ghz etc etc

So I'd like to know why performance in 3dmark seems to be better
 
Do you single core scores in say cpu-z increase or go down? I disable c-state on my ryzen 2600 to lock all cores to 3.7Ghz, feels faster but my single core benches go down a little bit compared the boost clock of 3.9Ghz
This is the reason.

To give a longer version: C-States are "idle" state levels for a CPU. This means that the power governor in the OS will say "oh, this CPU can't IDLE; ok then, keep on running". So, whenever a task is bounced by the scheduler to any given core, it will be running at full speed, so there's no "speed up" switching and will start working pretty much instantly. For benchmarks that spawn threads in rapid succession, this becomes a really noticeable uplift, even when the top speed is affected (cores can't go to IDLE -> more temperature -> less turbo speed up-time from P-States).

That being said, that uplift would be only noticeable in benchmarks and won't really net you overall increased performance, but will make your CPU run hot most of the time :)

Cheers!
 

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