The Performance Impact Of MDS / Zombieload Plus The Overall Cost Now Of Spectre/Meltdown/L1TF/MDS by Michael Larabel in Software on 18 May 2019. 28 Comments https://www.phoronix.com/scan.php?page=article&item=mds-zombieload-mit&num=1 "The past few days I've begun exploring the performance implications of the new Microarchitectural Data Sampling "MDS" vulnerabilities now known more commonly as Zombieload. As I shared in some initial results, there is a real performance hit to these mitigations. In this article are more MDS / Zombieload mitigation benchmarks on multiple systems as well as comparing the overall performance impact of the Meltdown / Spectre / Foreshadow / Zombieload mitigations on various Intel CPUs and also AMD CPUs where relevant. While disabling Hyper Threading now is recommended by multiple parties if running untrusted code on the system, even if keeping HT/SMT active, the MDS mitigations do provide a very noticeable performance hit in many real and synthetic workloads with the updated Linux kernel patches paired with the newest Intel CPU microcode. Like the other mitigations to this point, the workloads affected most are those with lots of context switches / high interactivity between kernel and user-space. Before getting to the benchmarks looking at the overall impact of the mitigations to date, first is looking at the MDS on/off costs on various systems while keeping Hyper Threading active. These tests were done on Ubuntu 19.04 using its newest stable release updates bringing a patched Linux 5.0 kernel and the new Intel CPU microcode images. I tested the MDS on/off tests with a few distinctly different systems for seeing the mitigation cost for Zombieload. Following this batch of tests is a larger set of tests looking at no mitigations for the CPU vulnerabilities, the default mitigations, and then the default mitigations with Hyper Threading disabled. All of these benchmarks were carried out using the Phoronix Test Suite." There are lots of graphs and supporting information (10 pages), please check out the results of his extensive testing at the URL above... "If looking at the geometric mean for the tests run today, the Intel systems all saw about 16% lower performance out-of-the-box now with these default mitigations and obviously even lower if disabling Hyper Threading for maximum security. The two AMD systems tested saw a 3% performance hit with the default mitigations. While there are minor differences between the systems to consider, the mitigation impact is enough to draw the Core i7 8700K much closer to the Ryzen 7 2700X and the Core i9 7980XE to the Threadripper 2990WX. More Linux mitigation benchmarks are coming up on Phoronix in the days ahead." 28 Comments Gaming Performance Only Faintly Touched By MDS / Zombie Load Mitigations by Michael Larabel in Linux Gaming on 17 May 2019 at 01:31 PM EDT. 14 Comments https://www.phoronix.com/scan.php?page=news_item&px=Zombie-Load-Gaming-Impact "Yesterday I published some initial MDS/Zombieload mitigation impact benchmarks while coming out still later today is much more data looking at the CPU/system performance impact... But is the gaming performance impaired by this latest set of CPU side-channel vulnerabilities? With the Spectre/Meltdown mitigations, the gaming performance fortunately wasn't impaired by those mitigations. In fact, it was pretty much dead flat. With my testing thus far of the MDS/Zombieload mitigations on Linux, there does appear to be a slight difference in the rather CPU-bound scenarios compared to Spectre/Meltdown, but still it should be negligible for gamers. Well, that is at least with the higher-end hardware tested thus far, over the weekend I'll be running some gaming tests on some low-end processors/GPUs. From the tests ran so far with the high-end parts, having the MDS mitigations active only would cause a frame or few hit in the rather CPU-bound scenarios. In those cases already, the games tend to run well over one hundred frames per second so would likely not be noticeable at all to gamers. ...check out the website for results... So maybe a ~1% hit for some Linux games (if that in some configurations) as a result of the new default MDS mitigations and stopping short of disabling Hyper Threading, but even there most Linux games at least don't use more than a few cores/threads. But as said, will have some low-end Linux gaming hardware tests out in the days ahead. More of the CPU/system benchmarks that are much more interesting in the context of these mitigations will be out shortly where it seems to be commonly 4~5% but more significant in the context switching heavy workloads." 14 Comments xfcemint Junior Member Join Date: May 2019 Posts: 38 #3 05-17-2019, 03:14 PM "I think the article should have made it more clear that this is with HT on. To really mitigate ZombieLoad, you need HT off. Although I speculate that for games, in most cases there will be little difference. But, for the sake of clarity and to provide non-confusing data, you always have to do a run with HT off, and to clearly note it in the article. Well, in fact, it is also going to depend on number of CPU cores. If a game needs more than 2 cores, and the CPU cannot provide them, there might be some performance hits."