With Hyper Threading continuing to look increasingly unsafe in data centers / shared computing environments in light of all the speculative execution vulnerabilities exposed thus far particularly with L1TF and MDS having no SMT-secure mitigation, DigitalOcean continues working on their Linux kernel "core scheduling" patches so they can still make use of HT/SMT in a sane and safe manner.

DigitalOcean's core scheduling work is their way to make Hyper Threading safe by ensuring that only trusted applications run concurrently on siblings of a core. Their scheduler also tries to be smart about not using SMT/HT in areas where it could degrade performance.

DigitalOcean engineers were at this week's Linux Plumbers Conference 2019 in Portugal talking about this ongoing work. DigitalOcean's preliminary tests have been encouraging that their core scheduling work can perform similar to the baseline in CPU results and better than just disabling Hyper Threading. But for I/O results like running a MySQL database server the performance has been worse than turning SMT off.

Those wanting to learn more about Core Scheduling can see this PDF slide deck from LPC 2019.