8 Jan
2018
8 Jan
'18
6:26 p.m.
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