Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 2 Dec 2016 09:53:52 -0800 | Subject | Re: [PATCH v2 5/6] x86/xen: Add a Xen-specific sync_core() implementation |
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On Fri, Dec 2, 2016 at 9:38 AM, Andy Lutomirski <luto@kernel.org> wrote: > > apply_alternatives, unfortunately. It's performance-critical because > it's intensely stupid and does sync_core() for every single patch. > Fixing that would be nice, too.
So looking at text_poke_early(), that's very much a case that really shouldn't need any "sync_core()" at all as far as I can tell.
Only the current CPU is running, and for local CPU I$ coherence all you need is a jump instruction, and even that is only on really old CPU's. From the PPro onwards (maybe even Pentium?) the I$ is entirely serialized as long as you change the data using the same linear address.
So at most, that function could mark itsel f"noinline" just to guarantee that it will cause a control flow change before returning. The sync_core() seems entirely bogus.
Same goes for optimize_nops() too.
Linus
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