linux-kernel - Re: [PATCH 1/4] brcm80211: deinline brcmf_chip_cr4

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Message-ID: <533970DF.70303@broadcom.com>
Date:	Mon, 31 Mar 2014 15:42:55 +0200
From:	Arend van Spriel <arend@...adcom.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>,
	Franky Lin <frankyl@...adcom.com>,
	Hante Meuleman <meuleman@...adcom.com>,
	"John W. Linville" <linville@...driver.com>,
	<linux-kernel@...r.kernel.org>, <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH 1/4] brcm80211: deinline brcmf_chip_cr4_enterdl, save
 440 bytes

On 31/03/14 13:18, Denys Vlasenko wrote:
> On 03/31/2014 09:38 AM, Arend van Spriel wrote:
>> On 30/03/14 23:31, Denys Vlasenko wrote:
>>> Automated script discovered that without forced inlining,
>>> gcc-4.7 generates smaller code for this function.
>>>
>>> There is no need to declare static functions inline anyway:
>>> nowadays gcc detects single-callsite static functions
>>> which benefit from inlining.
>>
>> These patches look awfully familiar. I tend to object, but I don't know the details of this automated script.
>
> The script removes "static" keyword, recompiles the .c file,
> compares the sizes, and if code size went down,
> creates a patch
>
>> How about execution time or is this only compile tested?
>
> The change adds one pair of call/return instructions -
> probably around 5-10 CPU cycles.
>
> The function in question is a part of firmware download logic,
> which is nowhere near being hot path/.

True. My remarks are on all four patches and I just replied to the first 
patch. The other patches are in interrupt handling code, ie. interrupt 
or bottom-halve context.

>> The other thing is that you seem to rely on a specific gcc version.
>> What about pre-4.7? How about different architectures.
>> Was this determined on x86, arm, sparc, mips.
>> All these questions make me say 'nay'.
>
> Not making functions inline unless there is a good reason
> is a general good coding practice. It is not a compiler-
> or architecture-specific optimization.

Agree, but you seem to assume that in this case there is no good reason.

Regards,
Arend


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