Hi Yves-Alexis, On Mon, Jan 08, 2018 at 06:07:54PM +0100, Yves-Alexis Perez wrote: > On Sun, 2018-01-07 at 11:18 +0100, Willy Tarreau wrote: > > - the highest performance impact on VMs comes from having PTI on the > > guest kernel (-45%). At this point it makes no difference whether > > the host kernel has it or not. > > Hi Willy, > > out of curiosity, is the pcid/invpcid flags exposed to and used by your guest > CPU? It might very well that the PCID optimisations are not used by the guests > here, and it might be worth either checking on bare metal or with the PCID > optimisations enabled.
You're totally right, I discovered during my later developments that indeed PCID is not exposed there. So we take the hit of a full TLB flush twice per syscall. Willy
