There's also the option of not running KPTI at all... database servers are the most heavily impacted, and since they only run trusted code there's not much point in patching them.
Re:CPU utilization is wrong [video]
by dragontamer on Monday April 30, 2018 @03:44PM
(#16961607)
Hmmm... I don't like the idea of disabling security for performance.
I'm not an expert on this, but I'd turn on Huge Tables (1GB) first. Big databases / datasets across RAM can be manipulated in 1GB chunks by the OS instead of 4kB (!!!) chunks. The Skylake CPU can only cache ~4 Huge Tables, but an additional set of Large Tables (2MB) should also help performance. If properly configured of course.
I would hope that those changes would mitigate most of the KPTI issues with regards to databases. But I really don't know.
In particular, the Linux KPTI (https://en.wikipedia.org/wiki/Kernel_page-table_isolation) which prevents Meltdown from affecting the Kernel. The hardware fix is simple: buy AMD Epyc instead. At least, in the nearterm. Intel's "Icelake" system will have the hardware fix so that KPTI can die sometime in 2019. Its not normal to flush the TLB on every systemcall. But its a necessary precaution as long as the CPU is vulnerable to Meltdown.