Messages in this thread | | | Date | Thu, 7 Apr 2011 10:08:25 +0200 | From | Ingo Molnar <> | Subject | Re: [RFT/PATCH v2 1/6] x86-64: Clean up vdso/kernel shared variables |
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* Andy Lutomirski <luto@MIT.EDU> wrote:
> Variables that are shared between the vdso and the kernel are > currently a bit of a mess. They are each defined with their own > magic, they are accessed differently in the kernel, the vsyscall page, > and the vdso, and one of them (vsyscall_clock) doesn't even really > exist. > > This changes them all to use a common mechanism. All of them are > delcared in vvar.h with a fixed address (validated by the linker > script). In the kernel (as before), they look like ordinary > read-write variables. In the vsyscall page and the vdso, they are > accessed through a new macro VVAR, which gives read-only access. > > The vdso is now loaded verbatim into memory without any fixups. As a > side bonus, access from the vdso is faster because a level of > indirection is removed.
Ok, that's a pretty nice consolidation and speedup.
This layout:
> +DECLARE_VVAR(0, volatile unsigned long, jiffies) > +DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data) > +DECLARE_VVAR(256, int, vgetcpu_mode)
Is spread out too much, using up several separate cachelines with nothing else on them. Why not pack it tightly, with natural alignment taken into consideration?
Thanks,
Ingo
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