netdev - Re: [PATCH v2 4/6] ath6kl: get rid of AR_DBG_LVL

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Date:	Fri, 6 Jan 2012 10:08:46 +0200
From:	Kalle Valo <kvalo@....qualcomm.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	<linville@...driver.com>, <sfr@...b.auug.org.au>,
	<netdev@...r.kernel.org>, <linux-wireless@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-next@...r.kernel.org>,
	<ath6kl-devel@...lcomm.com>, <davem@...emloft.net>
Subject: Re: [PATCH v2 4/6] ath6kl: get rid of AR_DBG_LVL_CHECK()

On 01/05/2012 04:14 PM, David Laight wrote:
> 
>> We don't need it as debug calls already have a log level and
>> compiler should be smart enough to optimise away the code when
>> ath6kl debug code is not enabled.
> 
> Have you checked?

No, I just assumed so.

> I think you are assuming that because the called function collapses,
> the call will be removed allowing the loop to be removed. I suspect
> this is only true if the function is inlined. IIRC the normal linkage
> rules mean that only static functions are candidates for inlining.

I think you are right.

But while I investigated more I noticed that ath6kl_dump_registers()
will be an empty static inline whenever CONFIG_ATH6KL_DEBUG is disabled
and that will make sure that the whole function is not included. So
whenever ath6kl debug code is enabled there is a small performance hit,
but it's so small that IMHO we don't need to worry about it.

And for optimal performance CONFIG_ATH6KL_DEBUG should be disabled anyway.

What do you think?

Kalle
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