Jak jsme již dnes psali, kernel 4.20 se záplatou STIBP proti Spectre v2 v přítomnosti HT je citelně pomalejší v některých zátěžích. K tématu se vyjádřil i Linus Torvalds.
This was marked for stable, and honestly, nowhere in the discussion did I see any mention of just *how* bad the performance impact of this was.
When performance goes down by 50% on some loads, people need to start asking themselves whether it was worth it. It's apparently better to just disable SMT entirely, which is what security conscious people do anyway.
So why do that STIBP slow-down by default when the people who *really* care already disabled SMT?
I think we should use the same logic as for L1TF: we default to something that doesn't kill performance. Warn once about it, and let the crazy people say „I'd rather take a 50% performance hit than worry about a theoretical issue“.
Pravděpodobně tedy záplata STIBP bude ve výchozím stavu vypnutá. Nepříjemné je, že zpomalující záplata STIBP se již dostala kromě 4.20 také do 4.19.2.
(zdroj: phoronix)
