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

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Message-ID: <alpine.LNX.2.00.1511270004570.20111@pobox.suse.cz>
Date:	Fri, 27 Nov 2015 00:05:17 +0100 (CET)
From:	Jiri Kosina <jikos@...nel.org>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
cc:	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: debug: improve hid_debug_event()

On Tue, 24 Nov 2015, Rasmus Villemoes wrote:

> The code in hid_debug_event() causes horrible code generation. First,
> we do a strlen() call for every byte we copy (we're doing a store to
> global memory, so gcc has no way of proving that strlen(buf) doesn't
> change). Second, since both i, list->tail and HID_DEBUG_BUFSIZE have
> signed type, the modulo computation has to take into account the
> possibility that list->tail+i is negative, so it's not just a simple
> and.
> 
> Fix the former by simply not doing strlen() at all (we have to load
> buf[i] anyway, so testing it is almost free) and the latter by
> changing i to unsigned. This cuts 29% (69 bytes) of the size of the
> function.
> 
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

Agreed, this is much better. Applied to for-4.5/core, thanks Rasmus.

-- 
Jiri Kosina
SUSE Labs

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