Spectre/Meltdown/L1TF/MDS Mitigation Costs On An Intel Dual Core + HT Laptop
Written by Michael Larabel in Hardware on 21 May 2019 at 08:19 AM EDT. 26 Comments
HARDWARE --
Following the recent desktop CPU benchmarks and server CPU benchmarks following the MDS/ZombieLoad mitigations coming to light and looking at the overall performance cost to mitigating these current CPU vulnerabilities, there was some speculation by some in the community that the older dual-core CPUs with Hyper Threading would be particularly hard hit. Here are some benchmarks of a Lenovo ThinkPad with Core i7 Broadwell CPU looking at those mitigation costs.


Here are some quick complementary data points looking at the impact of the mitigations=off / mitigations=auto (the default kernel behavior for these mitigations) / mitigations=auto,nosmt (disabling Hyper Threading) when using a Core i7 5600U with two physical cores plus Hyper Threading, very different from the desktop/server CPU benchmarks in recent days with high core counts.

Ubuntu 19.04 was in use with the patched Linux 5.0 kernel.

The I/O cost remains high as usual.

Memory allocations can take longer as well.





The socket impact is particularly high.

As seen with the beefier CPUs, the Hackbench Linux kernel scheduler is particularly hard hit by these mitigations.





GIMP and Darktable are among the real-world desktop applications seeing a difference from these default mitigations and obviously more so once HT gets flipped off.

The MATLAB-like Octave software is another one of those affected applications.



Context switching on this Core i7 Broadwell CPU takes seven times longer since these mitigations.


The JavaScript/browser performance on this dual-core laptop also sees a hit from the default mitigations even if keeping HT enabled.

If looking at the geometric mean across dozens of benchmarks ran, the default/out-of-the-box mitigations dropped the performance by 18% or 25% when disabling Hyper Threading. See all the benchmarks via this OpenBenchmarking.org result file.
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Michael Larabel is the principal author of Phoronix.com and founded the site in 2004 with a focus on enriching the Linux hardware experience. Michael has written more than 20,000 articles covering the state of Linux hardware support, Linux performance, graphics drivers, and other topics. Michael is also the lead developer of the Phoronix Test Suite, Phoromatic, and OpenBenchmarking.org automated benchmarking software. He can be followed via Twitter or contacted via MichaelLarabel.com.

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