Messages in this thread |  | | Date | Fri, 02 Sep 2011 14:42:21 -0700 | | From | Jeremy Fitzhardinge <> | | Subject | Re: [PATCH 00/13] [PATCH RFC] Paravirtualized ticketlocks |
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On 09/02/2011 01:27 PM, Linus Torvalds wrote: > On Fri, Sep 2, 2011 at 1:07 PM, Jeremy Fitzhardinge <jeremy@goop.org> wrote: >> I don't know whether that fastpath code is small enough to consider >> inlining everywhere? > No. > > There's no point in inlining something that ends up containing a > conditional function call: gcc will have to effectively save/restore > registers around that thing anyway, so you lose a lot of the > advantages of inlining. So I think it's better done as an out-of-line > function, which I thought we did for spinlocks anyway.
Yes, lock currently out-of-line.
I should also make sure that unlock is also out of line when paravirtualized.
> Also, do you run with CONFIG_OPTIMIZE_SIZE? Without that, gcc should > be smart enough to make a "likely()" case be a fall-through.
Ah, I was wondering why I'd never seen likely/unlikely do anything useful. With OPTIMIZE_SIZE=n, there's no point in explicitly moving the slowpath out to a separate function.
So the only downside with this variant is that it breaks my design criteria of making the generated code look identical to the the original code when CONFIG_PARAVIRT_SPINLOCKS=n. But I don't know if that's an actual downside in practice.
J
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