at 7:11 AM, Andy Lutomirski <[email protected]> wrote: > > > On Oct 3, 2018, at 9:59 PM, Nadav Amit <[email protected]> wrote: > >> This RFC proposes to return part of the entry-area back to the fixmap to >> improve system-call performance. Currently, since the entry-area is >> mapped far (more than 2GB) away from the kernel text, an indirect branch >> is needed to jump from the trampoline into the kernel. Due to Spectre >> v2, vulnerable CPUs need to use a retpoline, which introduces an >> overhead of >20 cycles. > > That retpoline is gone in -tip. Can you see how your code stacks up against > -tip? If it’s enough of a win to justify the added complexity, we can try > it. > > You can see some pros and cons in the changelog: > > https://git.kernel.org/tip/bf904d2762ee6fc1e4acfcb0772bbfb4a27ad8a6
Err.. That’s what I get for not following lkml. Very nice discussion. Based on it, I may be able to do an additional micro-optimizations or two. Let me give it a try.
