linux-kernel - RE: [PATCH 1/2] rtlwifi: Fix improve function 'rtl_addr

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D1CCD61C8@AcuExch.aculab.com>
Date:	Thu, 4 Feb 2016 09:48:34 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Larry Finger' <Larry.Finger@...inger.net>,
	ByeoungWook Kim <quddnr145@...il.com>
CC:	"kvalo@...eaurora.org" <kvalo@...eaurora.org>,
	"chaoming_li@...lsil.com.cn" <chaoming_li@...lsil.com.cn>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] rtlwifi: Fix improve function 'rtl_addr_delay()' in
 core.c

From: Larry Finger
> Sent: 03 February 2016 19:45
...
> The performance will depend on where you satisfy the condition. All switch cases
> have the same execution time, but in the if .. else if .. else form, the earlier
> tests execute more quickly. I'm not sure that one can make any blanket statement
> about performance. Certainly, the switch version will be larger. For a switch
> with 8 cases plus default, the object code if 43 bytes larger than the nested
> ifs in a test program that I created. That is a significant penalty.

There is also the penalty of the (likely) data cache miss reading the jump table.
But given this code is all about generating a variable delay the execution
speed is probably irrelevant.

It would be much more interesting if the delay could be changed for sleeps.

	David