From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5709CC3A5A1 for ; Thu, 22 Aug 2019 12:28:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2ABF7214DA for ; Thu, 22 Aug 2019 12:28:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731592AbfHVM2z (ORCPT ); Thu, 22 Aug 2019 08:28:55 -0400 Received: from mail02.iobjects.de ([188.40.134.68]:38660 "EHLO mail02.iobjects.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727807AbfHVM2z (ORCPT ); Thu, 22 Aug 2019 08:28:55 -0400 Received: from tux.wizards.de (pD9EBF359.dip0.t-ipconnect.de [217.235.243.89]) by mail02.iobjects.de (Postfix) with ESMTPSA id 2A0AF4160376 for ; Thu, 22 Aug 2019 14:28:54 +0200 (CEST) Received: from [192.168.100.223] (ragnarok.applied-asynchrony.com [192.168.100.223]) by tux.wizards.de (Postfix) with ESMTP id C70F95C9997 for ; Thu, 22 Aug 2019 14:28:53 +0200 (CEST) Subject: Re: [PATCH v2 0/4] Support xxhash64 checksums To: Linux BTRFS Mailinglist References: <20190822114029.11225-1-jthumshirn@suse.de> From: =?UTF-8?Q?Holger_Hoffst=c3=a4tte?= Organization: Applied Asynchrony, Inc. Message-ID: Date: Thu, 22 Aug 2019 14:28:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20190822114029.11225-1-jthumshirn@suse.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 8/22/19 1:40 PM, Johannes Thumshirn wrote: > Now that Nikolay's XXHASH64 support for the Crypto API has landed and BTRFS is > prepared for an easy addition of new checksums, this patchset implements > XXHASH64 as a second, fast but not cryptographically secure checksum hash. Question from the cheap seats.. :) I know that crc32c-intel uses native SSE 4.2 instructions, but so far I have been unable to find benchmarks or explanations why adding xxhash64 benefits btrfs. All benchmarks seem to be against crc32c in *software*, not the SSE4.2-enabled version (or I can't read). I mean, it's great that xxhash64 is really fast for a software implementation, but how does btrfs benefit from this compared to using crc32-intel? Verifying that plugging in other hash impls works (e.g. as preparation for stronger impls) has value, but it's probably not something most users care about. Maybe there are obscure downsides to crc32c-intel like instruction latency (def. a problem for AVX512), cache pollution..? Just curious. thanks, Holger