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Intel Skylake μArch Analysis from IDF 2015



/ 1 year ago

Intel IDF 2015 CPU x86 Skylake 1

Despite launching the i7 6700K and i5 6600K based off the Skylake μArch earlier this month, Intel has kept the wraps on the μArch till IDF [Intel Developer Forum] 2015 today. We finally know what improvement and tweaks Intel has done to make Skylake a tad bit faster than Haswell.

Intel IDF 2015 CPU x86 Skylake 4

While Intel extracted more efficiency and added more execution units to Haswell, most of the information released from IDF so far points to improving efficiency rather than increasing the brute force power of the chip. First of all, the front end received a number of improvements, with the Out-of-order Window increased to 224 from 192, the In-flight Stores from 42 to 56, Scheduler Entries grew to 97 from 60, the Allocation Queue from 56 to 64 and the Integer Register File from 168 to 180. All of these small improvements should help feed the cores better and improve efficiency, leading to lower power consumption and better IPC. Specific instructions like AES-GCM and AES-CBC also improved by 17% and 33% respectively.

Intel IDF 2015 CPU x86 Skylake 2

Improvements were also made to other sections, with an improved ring bus, Last Level Cache and Hyper-Threading. These changes should help drive better multi-core efficiency, something that we’ve seen strong improvement in for multi-threaded tasks. This has been helped along with a better branch predictor, improved cache and buffer latency and bandwidth to feed the cores. Of course, the IMC is improved with support for DDR4 and the chipset is connected by the faster and wider DMI 3.0. As expected, power consumption also improved with better power gating of units in the cores, which should help reduce load temps if not all execution units are being used.

Intel IDF 2015 CPU x86 Skylake 3

While Intel already has a very wide core with Haswell, with 8 execution ports, Skylake reportedly increases that number as well. No information about that has yet been released though we will probably get more information as Skylake specific presentations roll out through the rest of IDF 2015. We’ll bring you more information about Skylake as they come. It’s interesting though that despite all these improvements, IPC has only increased by a few percent over Haswell. You can find the full set of day 1 Skylake slides here.


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