Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752101AbaBXKxQ (ORCPT ); Mon, 24 Feb 2014 05:53:16 -0500 Received: from nat28.tlf.novell.com ([130.57.49.28]:45624 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751509AbaBXKxP convert rfc822-to-8bit (ORCPT ); Mon, 24 Feb 2014 05:53:15 -0500 Message-Id: <530B32A4020000780011EACB@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.2 Date: Mon, 24 Feb 2014 10:53:08 +0000 From: "Jan Beulich" To: "Daniel Borkmann" Cc: , , , , , , Subject: Re: [PATCH 2/3] x86/hash: swap parameters of crc32_u32() References: <53073986020000780011E2E1@nat28.tlf.novell.com> <5308938A.8070506@redhat.com> <530B0AF2020000780011E97B@nat28.tlf.novell.com> <530B1D60.8010602@redhat.com> In-Reply-To: <530B1D60.8010602@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 24.02.14 at 11:22, Daniel Borkmann wrote: > On 02/24/2014 09:03 AM, Jan Beulich wrote: >>>>> On 22.02.14 at 13:09, Daniel Borkmann wrote: >>> On 02/21/2014 11:33 AM, Jan Beulich wrote: >>>> ... to match its two callers (i.e. the alternative would have been to >>>> swap the arguments at the call sites). >>>> >>>> Signed-off-by: Jan Beulich >>>> Cc: Francesco Fusco >>>> Cc: Daniel Borkmann >>>> Cc: Thomas Graf >>>> Cc: David S. Miller >>>> --- >>>> arch/x86/lib/hash.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> --- 3.14-rc3-x86-hash-crc32.orig/arch/x86/lib/hash.c >>>> +++ 3.14-rc3-x86-hash-crc32/arch/x86/lib/hash.c >>>> @@ -37,7 +37,7 @@ >>>> #include >>>> #include >>>> >>>> -static inline u32 crc32_u32(u32 crc, u32 val) >>>> +static inline u32 crc32_u32(u32 val, u32 crc) >>>> { >>>> #ifdef CONFIG_AS_CRC32 >>>> asm ("crc32l %1,%0\n" : "+r" (crc) : "rm" (val)); >>> >>> Can you elaborate? >>> >>> Sorry, I need to ask here (even if it's a stupid question ;)) if this >>> change is safe to do; are referring to a cleanup or fixing a concrete >>> bug? The code is a modified version of the DPDK hash which you can find >>> in [1]. Arguments of the caller are in the correct order, afaik. >>> >>> [1] http://dpdk.org/browse/dpdk/tree/lib/librte_hash/rte_hash_crc.h >> >> Yes, that file appears to be correct: >> >> rte_hash_crc_4byte(uint32_t data, uint32_t init_val) >> >> as opposed to >> >> static inline u32 crc32_u32(u32 crc, u32 val) >> >> (quite obviously data <-> val and crc <-> init_val, supported >> by the second argument in each caller being named "seed"). > > If you want a more descriptive name, feel free to rename these vars, > but check it yourself, it's not a bug as you claim; results are the > same: Even if the results are the same (operands being symmetric?), check the generated code for your version and the fixed up one: The crc32 instruction allows one of its operands to be in memory for a reason. Jan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/