Messages in this thread | | | Subject | Re: [PATCH v4 1/5] getcpu_cache system call: cache CPU number of running thread | From | "H. Peter Anvin" <> | Date | Tue, 1 Mar 2016 13:47:38 -0800 |
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On 03/01/16 13:32, Peter Zijlstra wrote: > On Tue, Mar 01, 2016 at 08:23:12PM +0000, Mathieu Desnoyers wrote: >> I think it's important that user-space fast-paths can quickly >> detect whether the feature is enabled without having to rely on >> always reading a separate cache-line. I've put together an ABI >> proposal that take into account the feedback received so far. > > Nah, adding detectoring code to fast paths is silly, makes them less > fast. Doesn't userspace have self modifying code? I know that at least > glibc does linker trickery to call different functions depending on > runtime context. >
No, userspace does not have self-modifying code. The glibc indirect function is done at dynamic link time; it is also worth noting that resolving global symbols through dynamic linking often requires an indirect call.
-hpa
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