Messages in this thread | | | Subject | Re: [PATCH v2 1/8] powerpc/32: Add VDSO version of getcpu | From | Christophe Leroy <> | Date | Tue, 29 Oct 2019 17:10:28 +0100 |
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Le 18/09/2019 à 07:51, Michael Ellerman a écrit : > > We are still in the middle of the years long process of removing the > "magic" syscall on 64-bit: > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/powerpc/kernel/exceptions-64s.S?commit=4d856f72c10ecb060868ed10ff1b1453943fc6c8#n1578 > > > Can we not add another one on 32-bit? > > Is it really such a fast path that it's worth putting a wart in the > syscall entry like that? > > Is there some other method? On s390 they have a per-cpu VDSO page, that > would be a nice option. How we do that would be specific to a particular > MMU, and maybe not even possible with some MMUs. So maybe that's not > feasible.
Ok, for now I remove the fast syscall and only keep the VDSO getcpu() for non SMP.
I think we may in the future implement a per-cpu VDSO page that will be mapped to the process based on the CPU it is running on. I need to look at that in more details.
Christophe
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