I had been holding my Win 8.1 workstation, which I use for my primary software engineering and business management work, at a December 2017 level of patching (i.e., I have avoided all core Windows Updates for it since December, though I have applied things like the Internet Explorer and Office updates).
Being at a good breakpoint a few days ago, and equipped with at least 4 different methods for restoring my system should I wish to do so, I applied the June core cumulative Windows 8.1 update. My system had run 50 days flawlessly without a reboot prior to that.
After the updates, benchmarks showed more than a 30% drop in overall performance, but 50% or more in the user interface (i.e., where you really feel it), and more than 30% in disk I/O operations. It turns out the Spectre and Meltdown mitigations are responsible for this, so I used the Gibson Research "InSpectre" tool to disable them. This caused the performance hit to drop to "only" 8%.
That is to say, my system performance was 8% lower overall than it was at the December patch level.
I have a number of both compute- and I/O-intensive jobs scheduled, for which I have good logs for recent runs. In particular, one build of a set of our software has been taking 47 minutes to complete. After the updates, the time jumped to 51 minutes - right in line with the 8% drop in performance the benchmarks showed.
I found the same exact thing with a Windows 7 hardware system. Exactly the same slowdown with those silly mitigations disabled - 8% - and much more with them enabled.
Is everyone just taking these performance hits without question or complaint?
Are folks really so scared of the well-developed marketing campaigns for things like Spectre and Meltdown that they will pay any price for (a false sense of) security?
-Noel