Re: [PATCH v2 32/36] x86/entry: Micro-optimize compat fast syscall arg fetch

[Ingo Molnar]

* Andy Lutomirski <luto@xxxxxxxxxx> wrote:

> we're following a 32-bit pointer, and the uaccess code isn't smart
> enough to figure out that the access_ok check isn't needed.
> 
> This saves about three cycles on a cache-hot fast syscall.

Another request: could you please stick the benchmarking code of the various x86 
system call variants into 'perf bench' - under tools/perf/bench/, so that 
measurements can be done on more hardware and can be reproduced easily?

I'd suggest we dedicate an entirely new benchmark family to it: 'perf bench x86' 
and then have:

   perf bench x86 syscall vdso
   perf bench x86 syscall int80
   perf bench x86 syscall vdso-compat

or so?

( I have some perf bench cleanups in -tip, so if you do this please base it on top 
  of that. )

Thanks,

	Ingo
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