linux-kernel - Re: [PATCH] HID: debug: improve hid_debug

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Message-ID: <87a8q0eamw.fsf@rasmusvillemoes.dk>
Date:	Thu, 26 Nov 2015 22:03:35 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Joe Perches <joe@...ches.com>
Cc:	Jiri Kosina <jikos@...nel.org>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: debug: improve hid_debug_event()

On Wed, Nov 25 2015, Joe Perches <joe@...ches.com> wrote:

>>  	spin_lock_irqsave(&hdev->debug_list_lock, flags);
>>  	list_for_each_entry(list, &hdev->debug_list, node) {
>> -		for (i = 0; i < strlen(buf); i++)
>> +		for (i = 0; buf[i]; i++)
>>  			list->hid_debug_buf[(list->tail + i) % HID_DEBUG_BUFSIZE] =
>>  				buf[i];
>>  		list->tail = (list->tail + i) % HID_DEBUG_BUFSIZE;
>
> trivia:
>
> The code might look nicer if (list->tail + i) % HID_DEBUG_BUFSIZE
> was stored into a temporary.

Maybe.

> Maybe use an if >= BUFSIZE to avoid a %

Nah, that would likely be worse; both a cmov and a conditional jump are
probably more expensive than a simple '& 0x1ff' which the % should compile to
(provided the expression is unsigned).

Rasmus
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