A bug in Intel’s processor architecture, reported by mathematicians at the Great Internet Mersenne Prime Search, could hang systems running Prime95 under very specific conditions.
A bug in Intel’s processor architecture, reported by mathematicians at the Great Internet Mersenne Prime Search, could hang systems running Prime95 under very specific conditions.
In December mathematicians at the Great Internet Mersenne Prime Search (aka GIMPS) reported the discovery of a reproducible bug in Intel‘s Skylake CPUs, confirmed after extensive testing triggered by reports from forum members at HardwareLuxx.de. Thankfully it now appears that Intel is in the process of rolling out a fix via BIOS updates, now being issued by motherboard vendors.
The bug, which occurs when running the popular Prime95 benchmarking software, only crops up in very specific system configurations – namely one with an Intel Core i7-6700K CPU, Hyperthreading Enabled, and a test run with the CPUsupportsFMA3 flag; it was however independent of OS, motherboard and DRAM vendor. Systems that ran foul of the bug either hung or exhibited aberrant behaviour, which is obviously distinctly sub-optimal when benchmarking or dealing with workloads that require speed and mathematical precision.
In the ensuing weeks Intel requested additional info to get to the root of the problem, which GIMPS naturally provided. The problem seemingly occurs only with newer versions (i.e. Version 28 and later) of Prime95 that utilise Intel’s Fused Multiply-Add instruction set; this feature has been included in Intel processors since Haswell, but the bug apparently doesn’t affect the older generation of processors. The narrowness of the bug explains why there hasn’t been a major outcry over this issue, and at present seems to be isolated to workloads peculiar to Prime95.
This week Arstechnica reported on the bug, and Intel themselves confirmed that the root cause had been uncovered and a fix was being pushed to CPUs via BIOS updates.
MSI Z170A GAMING M7
Today MSI contacted us to state that a new set of beta BIOS updates incorporating Intel’s fix for the problem are available for two of their high-performance motherboard SKUs, and that a comprehensive set of updated BIOS releases for all their motherboards based on Intel’s 100-series chipset are in the works. Users of the Z170A XPOWER GAMING TITANIUM and Z170A GAMING M7 motherboards who have a pressing need for the fix can find beta BIOS updates here; fully qualified BIOS updates will be available from the MSI website in the near future.
In general, the problem appears to occur in only a minority of configurations and under very rare conditions that aren’t related to either the majority of your hardware or any overclock you might be running. As a result it probably shouldn’t impact your decision whether or not to upgrade to Skylake, and any uncertainty will hopefully be rendered moot thanks to the efforts of Intel and motherboard vendors.
