VMware Engineer Revises Work On Concurrent TLB Flushes For Linux

After a two year hiatus on the patches, VMware's Nadav Amit has gotten back to working on concurrent TLB flushing support for the Linux kernel in yielding a small but measurable performance improvement.

Nadav has been working on Linux patches to allow for flushing of remote and local TLBs concurrently. Back in mid 2019 numbers shared by him pointed up to a 1~4% performance improvement on average under sysbench for these patches.

But the patches were not revised until recently when they were re-based against the Linux 5.11 kernel and then a second iteration of the patches to address some new bugs and other items brought up in the code review. So now this current TLB flushing support is up to the v6 iteration and hopefully on track for mainline, but is coming too late anyhow for the Linux 5.12 merge window already in progress.

VMware has been looking at TLB flushing changes over the years - including this concurrent flushing support - as part of the effort to reduce the overhead over Meltdown mitigations brought on with kernel page table isolation (KPTI). Assuming the patches don't fall through the cracks again, the concurrent remote/local TLB flushing could potentially be part of the 5.13 kernel this summer.