Memory, Cache, Throttling Benchmarks
For interest’s sake I’ve included the memory bandwidth results here for Kaby Lake-R, which are slightly improved on Kaby Lake thanks to DDR4-2400 support.
|CPU||L1 Cache Bandwidth||L2 Cache Bandwidth||L3 Cache Bandwidth|
|Core i7-8550U||640 MB/s||333 MB/s||180 MB/s|
|Core i7-7500U||376 MB/s||188 MB/s||105 MB/s|
|Core i7-7700HQ||780 MB/s||404 MB/s||209 MB/s|
|Core i7-6500U||324 MB/s||149 MB/s||92 MB/s|
|Core i7-5600U||309 MB/s||111 MB/s||62 MB/s|
Cache is a more interesting story, as Kaby Lake-R includes double the amount of cache as Kaby Lake across the board, and this comes with significantly faster bandwidth. The difference in cache bandwidth is enormous, and while it’s not quite at the level of the H-series Kaby Lake CPUs, it’s way more than a generational leap for the U-series.
PCIe lanes, however, remain at 12 so there is no significant gains to be seen in that department.
It's unlikely that you will experience the Core i7-8550U at its maximum turbo clock speed for any significant period of time. During our usage, we mostly found the CPU to sit in the 2.7 to 2.3 GHz range in intensive all-core workloads. You can see from the above graph, pass 1 of our x264 encode sat at around 2.6 GHz, while the more intensive second pass dropped to 2.3 GHz.
Short workloads can push clock speeds up to the maximum of 3.7 GHz, however you won't experience this under sustained loads. The good news is we never saw the CPU decrease all the way to the base frequency of 1.8 GHz: even under a super intensive x265 encode, the CPU still managed a clock of 2.1 GHz.