I will try to keep it as concise as possible.
- 8700K should boost up to 4700MHz/47x per one core. This is very easy to test if functional, through a monitoring app such as HWinfo64, High Performance power plan and a very light workload (i.e. lave the PC idle for a short while)
- expected, normal result on a correctly functioning CPU is that HWinfo64 will register the 47x multiplier and 4700MHz. As Turbo Boost is opportunistic, it is obviously not a stable 47x, but that doesn't matter - what matters is that at times, the properly cooled and installed CPU will reach 4700 MHz.
- the expected result occurs on a fresh Windows 10 x64 FCU (1709) installation. The CPU works correctly - 47x multi is reached
- after applying the first batch of updates (I'm positive it includes some Meltdown/Spectre mitigations, as before these patches were released my 8700K functioned normally. This is why I performed a fresh OS reinstall, to see if I can remedy the issue. No luck), the
CPU is only able to boost to 4600MHz/46x, regardless of workflow and conditions. Reinstalling the OS fixes it, but obviously you're left unpatched
- bug should be very easy to reproduce
Additional info I am not 100% certain of:
- the culprit is the Core0 multi. Through BIOS and MSI Command Center (app that allows you some OC inside the OS) I tried setting it higher than the default 47x. It does not work. That core will always boost to 46X max after updates
- allowing 2,3 or more cores to boost to 4.7 GHz fixes it. If you want to test this, I suggest using 3-4 cores, it seems that it would appear faster on HWinfo64 (again, High Perf power plan, leave it idle, or browse web/do something light).
- something like MCE (multicore turbo, has different names depending on vendor) would function normally. What is affected is the default, out of the box, non-OC 8700K.
- OC works as long as you don't try to OC Core0 to higher multis. That would simply not work, it remains at 46X. Any OC would have to be performed for 2 cores, as it seems to not possible (at least on my board) to use a 45x multi on Core0 and a 47X on Core1, for example
Would be nice to see an acknowledgement of this bug. I already confirmed it with others using 8700K at MSI forums and reported it to Microsoft as well, although they didn't seem to care much. Would also be nice to see it confirmed from other users.
Keep in mind Intel, this means your CPU performs worse out of the box, additionally to the Spectre/Meltdown impact, and it would affect buyers that will feel they didn't get what was advertised/seen in web reviews.
8700K, MSI Z370 Gaming Plus (BIOS 1.12, but it occurs on earlier BIOS too), GTX 1070Ti, 16 GB 3000 MHz DDR4 RAM.
The patches that were applied:
How it looks on a fresh OS (correct 47x):
How it looks on a patched OS: