Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A445AC433F5 for ; Mon, 13 Dec 2021 15:02:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239781AbhLMPCu (ORCPT ); Mon, 13 Dec 2021 10:02:50 -0500 Received: from mga12.intel.com ([192.55.52.136]:62476 "EHLO mga12.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233156AbhLMPCt (ORCPT ); Mon, 13 Dec 2021 10:02:49 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1639407769; x=1670943769; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=d66/ZKnntiz6Qzl3+3blt9/blWF7mbtEsJKpnyupkuw=; b=ZsIRFt6JJ0b34yM5zaAMq4siVlVen1NlV3vwM9ak4qaSrvuaYtIQlQ17 0qdBbetTHxrEcPbFF2BXj4rZPdNgZujrR5QBXQBVwytP7ocSX8wG1zTVg fJpORSvdtD5YpyhLIchzjhM23sVfadg9XTrR71IB10UiQL6/cqjf2isRZ moZU2SMVBhlT22Eyf52aM//n2RZx4eD7axHUpJ+4nAsDmiQM4sGlKs8At b3YKgjqqsdmOPCSnanXQpyHGwa+6+bzbVMXXD8LVfeGpcD9MOFjGYuTlk xDCjhl0qLPOa0+k29QUPSxYfCqXEgnT6KtMUQhKqzn7b2TD446xPRh8l1 Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10196"; a="218763410" X-IronPort-AV: E=Sophos;i="5.88,202,1635231600"; d="scan'208";a="218763410" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga106.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Dec 2021 07:02:27 -0800 X-IronPort-AV: E=Sophos;i="5.88,202,1635231600"; d="scan'208";a="752292686" Received: from chenb-mobl1.amr.corp.intel.com (HELO [10.212.210.237]) ([10.212.210.237]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Dec 2021 07:02:27 -0800 Subject: Re: [PATCH] x86/lib: Remove the special case for odd-aligned buffers in csum_partial.c To: David Laight , 'Noah Goldstein' , Eric Dumazet Cc: "tglx@linutronix.de" , "mingo@redhat.com" , Borislav Petkov , "dave.hansen@linux.intel.com" , X86 ML , "hpa@zytor.com" , "peterz@infradead.org" , "alexanderduyck@fb.com" , open list , netdev References: <45d12aa0c95049a392d52ff239d42d83@AcuMS.aculab.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <45d12aa0c95049a392d52ff239d42d83@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/13/21 6:43 AM, David Laight wrote: > There is no need to special case the very unusual odd-aligned buffers. > They are no worse than 4n+2 aligned buffers. > > Signed-off-by: David Laight > --- > > On an i7-7700 misaligned buffers add 2 or 3 clocks (in 115) to a 512 byte > checksum. > That is just measuring the main loop with an lfence prior to rdpmc to > read PERF_COUNT_HW_CPU_CYCLES. I'm a bit confused by this changelog. Are you saying that the patch causes a (small) performance regression? Are you also saying that the optimization here is not worth it because it saves 15 lines of code? Or that the misalignment checks themselves add 2 or 3 cycles, and this is an *optimization*?