Jeffrey Walton wrote: > The hardware is the same, but the OS was upgraded from Fedora 32 to > Fedora 33. The kernel and possibly intel-microcode have changed > between May 2020 and January 2021. > > I'm aware of this problem with AMD's RDRAND and RDSEED, but it doesn't > affect Intel machines: > https://bugzilla.kernel.org/show_bug.cgi?id=85911 (so there should not > be any remediations in place). > > My question is, is anyone aware of what may be responsible for the > performance loss?
Intel messed up RDRAND security. Microcode fix to avoid data leak includes getting exclusive lock on some processor internal bus or something like that. That can be used as DoS tool: run those RDRAND instructions in tight loop, and all code execution on that CPU does slows down significantly. https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00320.html -- Jari Ruusu 4096R/8132F189 12D6 4C3A DCDA 0AA4 27BD ACDF F073 3C80 8132 F189
