From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-3.0 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI,RCVD_IN_SORBS_SPAM, RP_MATCHES_RCVD shortcircuit=no autolearn=no autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 42E0820958 for ; Thu, 23 Mar 2017 22:22:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934719AbdCWWWl (ORCPT ); Thu, 23 Mar 2017 18:22:41 -0400 Received: from mail-io0-f178.google.com ([209.85.223.178]:35936 "EHLO mail-io0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934707AbdCWWWj (ORCPT ); Thu, 23 Mar 2017 18:22:39 -0400 Received: by mail-io0-f178.google.com with SMTP id l7so6661942ioe.3 for ; Thu, 23 Mar 2017 15:22:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=ofENuUpMtUwoBg94DFDrU2TA/YyqGNFlM9kPfSXsfaM=; b=TzHXN/QIwV4uGPHkf8NGPuMV22PdMPAhBnxOWEO65YXArMh4N2CretYX8OTXORd/b9 NA7vxH0gbh/DJgb6V1SyvkT4GECv3OLmjpxDHzhrVgug876xTitfoKMj48N41Y4hGsvD SVLqGYj6j43WMGrvCqHvzIDY4UHSnY/uEuCt6/dzav2TAqQbzo4v3hLUuMT1CAosvqwP TIrdrYqL96Z6zVAHQ53r4J+EoORGN5QeAysO9c9AiOkzoLkOfzgg7m8HtvQOwmdYzaco YPN17R0qR1l3HXSi1z0eUwp05Oo8FB2kBfivgLXtFa8wMPCi9Vn+/DIPZ5OojaKC+mVf 66/Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ofENuUpMtUwoBg94DFDrU2TA/YyqGNFlM9kPfSXsfaM=; b=X1ZmVi7S1WjIdMpsuc63uWdn20AntP6X4WBF8/r1hSZ9CxOp/Duof6i4hYuSapaz8t gDG12tPlme+TMRw36xRW+UfBInaQbWfhQF+WgheqixnWyIoUW/i6NtuQcAaLWmQ30h3U rIjJ5VoFQNGsBLwLaSuIOIY4VUprZlNppaEeDkFpADKFuoNpBNQ1SUq0ARiTvndwDqWW DEBwIqI25p1l4ZHiUIAISvSDvKBgKBvzN/VTRClPKrvVtbtANFrCiZptez1VzYUGFe3w pOfKp6J31QymPLtt6n6XorxNfHWmWudP8KFJ9kIRSJSSZNpA/HX7K6HNfn/vyvNxzr8/ o9SQ== X-Gm-Message-State: AFeK/H3koAl+aC4NuPTp2VH+W98AeV2jgOHovSC2FUY/9YBJ9v2gBIWtj9Py/xD5UUINqw== X-Received: by 10.107.131.156 with SMTP id n28mr5892870ioi.39.1490307752447; Thu, 23 Mar 2017 15:22:32 -0700 (PDT) Received: from aiede.mtv.corp.google.com ([2620:0:1000:5b10:6c40:39b9:f9ab:ec6f]) by smtp.gmail.com with ESMTPSA id i7sm243187ioe.48.2017.03.23.15.22.31 (version=TLS1_2 cipher=AES128-SHA bits=128/128); Thu, 23 Mar 2017 15:22:31 -0700 (PDT) Date: Thu, 23 Mar 2017 15:22:29 -0700 From: Jonathan Nieder To: Johannes Schindelin Cc: Junio C Hamano , Lars Schneider , Jeff King , Git Mailing List , Linus Torvalds Subject: Re: USE_SHA1DC is broken in pu Message-ID: <20170323222229.GB20794@aiede.mtv.corp.google.com> References: <2B1DE627-11C8-4FA5-A354-76B6C475666A@gmail.com> <20170322220246.GD26108@aiede.mtv.corp.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Johannes Schindelin wrote: > On Wed, 22 Mar 2017, Jonathan Nieder wrote: > > Johannes Schindelin wrote: >>> As to the default of seriously slowing down all SHA-1 computations: >>> since you made that the default, at compile time, with no way to turn >>> on the faster computation, this will have a major, negative impact. >>> Are you really, really sure you want to do that? >>> >>> I thought that it was obvious that we would have at least a runtime >>> option to lessen the load. >> >> It's not obvious to me. I agree that the DC_SHA1 case can be sped up, >> e.g. by turning off the collision detection for sha1 calculations that >> are not part of fetching, receiving a push, or running fsck. > > And in those cases, using OpenSSL instead is *even* faster. [...] > The index is 300MB. If you have to experience a sudden drop in performance > of `git add`, even by "only" 30%, relative to OpenSSL, it is very > noticeable. It is painful. [...] > It gets even worse when it comes to fetching, let alone cloning. [...] > And by "switching collision detection off", I of course refer to *not* > using SHA1DC's routines at all, but what would have been used originally, > in Git for Windows' case: (hardware-accelerated) OpenSSL. > > Did I manage to clarify the problem? Yes. Thank you for explaining. Sincerely, Jonathan