Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [RFC] x86/cpu_entry_area: move part of it back to fixmap | Date | Thu, 4 Oct 2018 16:30:57 +0000 |
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at 7:11 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> > > On Oct 3, 2018, at 9:59 PM, Nadav Amit <namit@vmware.com> 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.
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