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Freon
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BCLK, non-K Skylake overclocking stories

Thu Jan 28, 2016 10:59 am

I have my secondary rig now up and running (already have a 6700K, etc. for a primary box).

i5-6500
BeQuiet Pure Rock cooler
Core V21 case
ASRock Z170M Extreme4
16GB Crucial something-or-other 2400mhz DDR4
Radeon 5770
Samsung 830 128GB, BX100 250GB drives

Currently running 130mhz BCLK for 4.16ghz with Vcore set to Offset, +150mV, and VCCSA, VCCIO, and I think PCH all to 1.2v (from 0.95 or 1.05 defaults?). Crashed at +100mV Vcore. Haven't tweaked too much to see which of those voltages besides Vcore are really required since the last step before it stopped crashing was upping Vcore. I was able to get it to run at 105mhz on the stock cooler and 115mhz with the Pure Rock without even touching any voltage settings, just adjusting memory clock to be close to the rated speed. Didn't really test the limits, though.

HWMon shows about 1.28v nominal and 1.296v peak Vcore. I don't really care to push it a whole lot further, probably stop about the same as my other Skylake box around 1.32 or so which lets that run 4.7ghz, looking like I won't quite get that high on this one but 4.4ghz or so looks reasonable and is probably plenty fast for the OBS and general screwing around I'll be doing with this machine. Might eventually spring for a 750 Ti or something so it can at least do some light gaming, but this build is more for taking over to a friends place to screw around with OBS and green screening.
 
chuckula
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Re: BCLK, non-K Skylake overclocking stories

Thu Jan 28, 2016 11:05 am

Very interestly. From the reports, it looks like the IGP gets disabled (you obviously have a regular GPU) but there were some rumors that AVX also got disabled with this type of overclocking. Can you run a PRIME95 or other AVX-enabled program to check if AVX is actually operational or disabled?
4770K @ 4.7 GHz; 32GB DDR3-2133; GTX-1080; 512GB 840 Pro (2x); Fractal Define XL-R2; NZXT Kraken-X60
--Many thanks to the TR Forum for advice in getting it built.
 
biffzinker
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Re: BCLK, non-K Skylake overclocking stories

Thu Jan 28, 2016 6:59 pm

Found this when I was searching on duckduckgo,
In an interesting article on overclocking the Core i5 6400 non-K processor, Hardware.fr has a closer look at the poor AVX2 performance of the overclocked non-K processors. They ran a couple of tests including the Intel LINPACK suite and a x265 encoding benchmark. They find the performance to be significantly lower when using the OC BIOS compared to the regular BIOS. For LINPACK the performance going up from 3.1GHz to 4.5GHz drops from 178 to 62 Gflops and the x265 performance drops from 5.89 to 4.68 images/s. Why? Power saving.

The site references an entry on Agner's CPU blog which details how the Skylake processors deal with 256-bit vector instructions. Quote: "I observed an interesting phenomenon when executing 256-bit vector instructions on the Skylake. There is a warm-up period of approximately 14 µs before it can execute 256-bit vector instructions at full speed. Apparently, the upper 128-bit half of the execution units and data buses is turned off in order to save power when it is not used. As soon as the processor sees a 256-bit instruction it starts to power up the upper half. It can still execute 256-bit instructions during the warm-up period, but it does so by using the lower 128-bit units twice for every 256-bit vector. The result is that the throughput for 256-bit vectors is 4-5 times slower during this warm-up period. If you know in advance that you will need to use 256-bit instructions soon, then you can start the warm-up process by placing a dummy 256-bit instruction at a strategic place in the code. My measurements showed that the upper half of the units is shut down again after 675 µs of inactivity."

Since the non-K overclocking capabilities disable any form of power management, it appears that Skylake processors are not able to enable the upper 128-bit half of the execution units.

Image
Source: Non-K Skylake Overclocking Hurts AVX2 Performance, Problem Related to "256-bit Vector Warm-up" HWBOT
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Freon
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Re: BCLK, non-K Skylake overclocking stories

Fri Jan 29, 2016 9:29 pm

Prime95 runs fine. Its menu says my CPU supports AVX and AVX2. I'll see if I can test Linpack.
 
Freon
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Re: BCLK, non-K Skylake overclocking stories

Fri Jan 29, 2016 10:06 pm

Did some quick tests with Linpack. I just modified the default runme_xeon64_ao.bat to set threads = 4 and ran it. i5-6500 @ 4.16 ghz shows around 40-50gflops, my 6700K @ 4.7ghz shows more like 225-240 gflops. I'm not sure if I'm running this right, it seems to run off into la-la land, so I let it run a bit then CTRL-C out of it. Doesn't seem to impact results much based on how long I let it run. The i5 isn't gett very warm, barely hits 50C. The i7 shoots up to ~75C but sometimes drops to ~45C for brief moments, not sure whats up with that.

*shrugs* Not sure I care that much about Linpack. I'll give some h.264 and h.265 encode jobs with handbrake a go.

i7:
Number of tests: 22

Maximum memory requested that can be used=3379418368, at the size=45056

=================== Timing linear equation system solver ===================

Size   LDA    Align. Time(s)    GFlops   Residual     Residual(norm) Check
2048   2112   4      0.062      92.9749  4.666240e-012 3.837310e-002   pass
2048   2112   4      0.061      94.0117  4.666240e-012 3.837310e-002   pass
2048   2112   4      0.059      96.6230  4.666240e-012 3.837310e-002   pass
4096   6208   4      0.258      177.6828 1.497180e-011 3.099301e-002   pass
4096   6208   4      0.261      175.4688 1.497180e-011 3.099301e-002   pass
4096   6208   4      0.256      178.8359 1.497180e-011 3.099301e-002   pass
6144   6208   4      0.710      217.8686 3.388778e-011 3.153140e-002   pass
6144   6208   4      0.704      219.6700 3.388778e-011 3.153140e-002   pass
6144   6208   4      0.697      221.9138 3.388778e-011 3.153140e-002   pass
8192   8256   4      1.609      227.8738 7.127343e-011 3.739978e-002   pass
8192   8256   4      1.611      227.5197 7.127343e-011 3.739978e-002   pass
8192   8256   4      1.610      227.6958 7.127343e-011 3.739978e-002   pass
10240  10304  4      2.980      240.2569 1.042863e-010 3.507777e-002   pass


i5:
Number of tests: 22

Maximum memory requested that can be used=3379418368, at the size=45056

=================== Timing linear equation system solver ===================

Size   LDA    Align. Time(s)    GFlops   Residual     Residual(norm) Check
2048   2112   4      0.552      10.3849  4.666240e-012 3.837310e-002   pass
2048   2112   4      0.812      7.0634   4.666240e-012 3.837310e-002   pass
2048   2112   4      0.767      7.4804   4.666240e-012 3.837310e-002   pass
4096   6208   4      2.304      19.8984  1.497180e-011 3.099301e-002   pass
4096   6208   4      2.238      20.4839  1.497180e-011 3.099301e-002   pass
4096   6208   4      2.342      19.5733  1.497180e-011 3.099301e-002   pass
6144   6208   4      5.268      29.3641  3.388778e-011 3.153140e-002   pass
6144   6208   4      5.139      30.1018  3.388778e-011 3.153140e-002   pass
6144   6208   4      5.045      30.6649  3.388778e-011 3.153140e-002   pass
8192   8256   4      10.071     36.4064  7.127343e-011 3.739978e-002   pass
8192   8256   4      9.988      36.7074  7.127343e-011 3.739978e-002   pass
8192   8256   4      8.411      43.5888  7.127343e-011 3.739978e-002   pass
10240  10304  4      16.583     43.1778  1.042863e-010 3.507777e-002   pass
 
chuckula
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Re: BCLK, non-K Skylake overclocking stories

Fri Jan 29, 2016 10:22 pm

Freon wrote:
Did some quick tests with Linpack. I just modified the default runme_xeon64_ao.bat to set threads = 4 and ran it. i5-6500 @ 4.16 ghz shows around 40-50gflops, my 6700K @ 4.7ghz shows more like 225-240 gflops.


Yeah, it looks like your AVX units & FMA3 are being deactivated there. Those scores are substantially lower than what I would expect even from the i5-6500 at stock, much less running overclocked. That probably also explains why your temps are hardly breaking a sweat, so at least you don't have to worry about AVX workloads melting your CPU :P
4770K @ 4.7 GHz; 32GB DDR3-2133; GTX-1080; 512GB 840 Pro (2x); Fractal Define XL-R2; NZXT Kraken-X60
--Many thanks to the TR Forum for advice in getting it built.
 
Freon
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Re: BCLK, non-K Skylake overclocking stories

Sun Feb 07, 2016 12:40 pm

Despite the announcement that ASRock is pulling SkyOC it appears it is still available:
http://www.asrock.com/mb/Intel/Z170M%20 ... p?cat=Beta

The BIOS for my board is still available. I checked the md5 with the version I downloaded a few weeks ago and it has not been modified.

Z17MX4_1.35 md5 2ad7a44ae7b69cfea8d47a1e7ba66edf
 
Freon
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Re: BCLK, non-K Skylake overclocking stories

Sun Feb 07, 2016 1:06 pm

Non-beta 1.40 BIOS is still present as well, and allows me to BCLK overclock. Linpack speed still hampered but CPUZ confirms the overclock sticks. So much for them pulling the SkyOC BIOS?
 
vargis14
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Re: BCLK, non-K Skylake overclocking stories

Sun Feb 07, 2016 3:26 pm

Even if they all get pulled their are so many people who have saved the Bio's for most all manufacturers foresaw the Bios lock would be applied to most manufacturers from pressure from Intel, But they will still be available through some googling from all the people who already downloaded the particular Bios that will allow Blk OCing I am sure.
Yay for the internet!:)
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