Messages in this thread | | | Date | Thu, 21 May 2015 01:36:12 -0700 | From | Brian Norris <> | Subject | Re: [PATCH] mtd: cfi: Deiline large functions |
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On Thu, May 21, 2015 at 09:50:38AM +0200, Denys Vlasenko wrote: > On 05/20/2015 08:56 PM, Brian Norris wrote: > > On Mon, May 18, 2015 at 12:58:40PM +0200, Denys Vlasenko wrote: > >> With this .config: http://busybox.net/~vda/kernel_config, > >> after uninlining these functions have sizes and callsite counts > >> as follows: > > > > Most of this is probably good, thanks. But I'm curious about one: > > > >> cfi_udelay(): 74 bytes, 26 callsites > > > > ^^ This is pretty dead-simple. If it's generating bad code, we might > > look at fixing it up instead. Almost all of its call sites are with > > constant input, so it *should* just become: > > > > udelay(1); > > cond_resched(); > > > > in most cases. For the non-constant cases, we might still do an > > out-of-line implementation. Or maybe we just say it's all not worth it, > > and we just stick with what you have. But I'd like to consider > > alternatives to out-lining this one. > > You want to consider not-deinlining (IOW: speed-optimizing)
Inlining isn't always about speed.
> a *fixed time delay function*? > > Think about what delay functions do...
I wasn't really looking at speed. Just memory usage.
And I was only pointing this out because udelay() has a different implementation for the __builtin_constant_p() case. You can't take advantage of that for non-inlined versions of cfi_udelay().
But that may be irrelevant anyway, now that I think again. At best, you're trading one function call (arm_delay_ops.const_udelay() on ARM) for another (cfi_udelay()), since you can never completely optimize out the latter. And in fact, my suggestion yields extra inlined calls, due to the cond_resched().
Brian
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