From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH 2/3] grant-table: refactor grant copy to reduce duplicate code Date: Thu, 22 Jan 2015 16:04:04 +0000 Message-ID: <54C12D8402000078000585B3@mail.emea.novell.com> References: <1421777990-1122-1-git-send-email-david.vrabel@citrix.com> <1421777990-1122-3-git-send-email-david.vrabel@citrix.com> <54C11628020000780005831F@mail.emea.novell.com> <54C10C57.1090406@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YEKEn-00059a-Vd for xen-devel@lists.xenproject.org; Thu, 22 Jan 2015 16:04:06 +0000 In-Reply-To: <54C10C57.1090406@citrix.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel Cc: xen-devel@lists.xenproject.org, Keir Fraser , Ian Campbell , Tim Deegan List-Id: xen-devel@lists.xenproject.org >>> On 22.01.15 at 15:42, wrote: > On 22/01/15 14:24, Jan Beulich wrote: >>>>> On 20.01.15 at 19:19, wrote: >>> +static int gnttab_copy_buf(const struct gnttab_copy *op, >>> + struct gnttab_copy_buf *dest, >>> + const struct gnttab_copy_buf *src) >>> +{ >>> + s16 rc; >> >> An s16 local variable used as return value in a function returning >> int is kind of odd. Elsewhere there are also cases where the >> function return types are also s16. I don't think that's particularly >> efficient, and hence I think it should be changed in the places >> where you add new helpers even if the original code used s16 >> for that purpose. > > I was (trying to) use s16 where we return a GNTST_* value instead of the > usual -ERRNO. I can change them all to int if this is preferred > (although I not sure I get your efficiency argument). Operations on 16-bit registers are less efficient on x86 (due to the extra operand size prefix byte). On ARM I don't even know how they get carried out by the compiler, but there surely is no way to access the low 16 bits of a register by other than memory loads or stores. Jan