Phoronix founder and open source software engineer, Michael Larabel, discovered yet unexplained feature in the behavior of new 10nm Intel processors Tiger Lake… Instead of running faster after disabling protection against speculative execution vulnerabilities, Tiger Lake suddenly started to run slower, and often outperformed older processors.
The author of the study cannot explain what happened and suggests flaws in the current microcode of Tiger Lake processors. But he promises to continue research and try to figure out what is happening. After all, in theory, softening protection mechanisms deprives the processor of a whole spectrum “Crutches” and it should increase performance noticeably. And this turns out to be true for the Kaby Lake Refresh, Whiskey Lake and Ice Lake processors that took part in this experiment. But the Tiger Lake processor time and again showed performance degradation as soon as protection was disabled.
Image source: Phoronix
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In his research, Michael Larabel used four Dell XPS laptops with the aforementioned processors, including the Tiger Lake generation Core i7-1165G7. All laptops were installed with Ubuntu 20.10 operating system with Linux 5.8 kernel with all required patches to mitigate vulnerabilities of Intel processor architectures. Tiger Lake processors are already protected from some vulnerabilities, for example, against iTLB Multihit, while vulnerabilities such as Specter V1 and V4 still require microcode patches. So protection patches for Tiger Lake could be disabled using a kernel parameter «mitigations = off»as with all older microprocessors.
Image source: Phoronix
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Laptops with a clean system have been tested with both security enabled and the parameter «mitigations = off»weakening the defense. As expected, the older Kaby Lake R and Whiskey Lake processors showed a stronger difference between the two modes. The Ice Lake generation processor, as a newer one and with already partially hardware-implemented security fixes, showed a smaller variation between the normal and protected modes of operation. But the Tiger Lake processor, as mentioned above, was downright surprised by slowing down after gaining complete freedom from “Patch” security.
Image source: Phoronix
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In the performance comparison graphs, you can see for yourself how much the Tiger Lake Gen Core i7-1165G7 processor slows down after disabling protection. An explanation has yet to be found for this fact, but for now we can only state that something is wrong with this processor. More research graphs can be seen on the website Phoronix.
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