Tests on the first Intel processors running on its new Skylake architecture in early August gave some odd results regarding the performance of games using discrete graphics cards. In some benchmarks, both Haswell and Broadwell, the previous generation CPUs, performed marginally better than or tied with Skylake. When we wrote about Skylake, we mentioned that it was support for new memory and storage bandwidth, not pure CPU speed, that made it a valuable upgrade. Now we've got a bit more insight into why Skylake struggled to surpass its predecessors.
According to AnandTech, the FCLK (f-clock) wasn’t being set up properly during start-up. Asus helped explain the situation. The FCLK affects the transmission of data between CPU and GPU by controlling a ratio frequency setting which is tied to the BCLK (base frequency of the processor). It’s set at either 4x, 8x, or 10x for 400 MHz, 800 MHz, or 1000 MHz. Apparently the default setting of the FCLK is 800 MHz for Skylake processors; however, Intel’s recommended value for desktops was 1000 MHz, so the 10x ratio setting should be used. AnandTech understands that the 10x setting back in early August wasn’t functioning properly.
A few weeks after the initial launch, Intel’s firmware update 1168 allowed the 10x setting to be implemented at POST by motherboard manufacturers. Current owners will need to upgrade their firmware in order to get this change. According to AnandTech, Asus says that it will “have it enabled by default (at stock) on version 0801 on the Z170-A, with 090x versions of the BIOS providing a manual option inside the Tweakers’ Paradise sub-menu. ASRock by comparison, on the 1.70 BIOS for the Extreme7+, has an option to adjust the FCLK in the CPU configuration menu, but sets 800 MHz as default and requires adjusting to 1 GHz to make the change.”
AnandTech ran some new tests with the new settings enabled, and noted a “subtle difference.” “In almost every scenario where performance was worse (except the GTX 980 against the i7-5775C), the new FCLK setting makes a change. Across the board, moving from an 800 MHz value on FCLK to 1 GHz gave an increase no matter what the discrete graphics test. Previously where our individual benchmarks ranged from zero change through -1 percent, -2 percent down to -8 percent, most results move up slightly, usually under 1 percent, but some get a boost as high as 5 percent.”
Those aren't exactly world-shattering improvements, but they're a nice little bump for anyone who already owns a Skylake CPU.
