Messages in this thread | | | Date | Fri, 12 Feb 2016 21:10:11 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 00/33] Compile-time stack metadata validation |
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On Fri, Feb 12, 2016 at 12:32:06PM -0600, Josh Poimboeuf wrote: > What I actually see in the listing is: > > decl __percpu_prefix:__preempt_count > je 1f: > .... > 1: > call ___preempt_schedule > > So it puts the "call ___preempt_schedule" in the slow path.
Ah yes indeed. Same difference though.
> I also don't see how that would be related to the use of the asm > statement in the __preempt_schedule() macro. Doesn't the use of > unlikely() in preempt_enable() put the call in the slow path?
Sadly no, unlikely() and asm_goto don't work well together. But the slow path or not isn't the reason we do the asm call thing.
> #define preempt_enable() \ > do { \ > barrier(); \ > if (unlikely(preempt_count_dec_and_test())) \ > preempt_schedule(); \ > } while (0) > > Also, why is the thunk needed? Any reason why preempt_enable() can't be > called directly from C?
That would make the call-site save registers and increase the size of every preempt_enable(). By using the thunk we can do callee saved registers and avoid blowing up the call site.
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