linux-kernel - Re: [PATCH] mtd: cfi: Deiline large functions

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Message-ID: <555D8E4E.9030109@redhat.com>
Date:	Thu, 21 May 2015 09:50:38 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Brian Norris <computersforpeace@...il.com>
CC:	David Woodhouse <David.Woodhouse@...el.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Jingoo Han <jg1.han@...sung.com>,
	Aaron Sierra <asierra@...-inc.com>,
	Artem Bityutskiy <Artem.Bityutskiy@...ux.intel.com>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: cfi: Deiline large functions

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)
a *fixed time delay function*?

Think about what delay functions do...

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