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[209.85.167.48]) by smtp.gmail.com with ESMTPSA id n25sm322201ljj.42.2021.09.08.11.27.10 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Sep 2021 11:27:11 -0700 (PDT) Received: by mail-lf1-f48.google.com with SMTP id k13so6705997lfv.2 for ; Wed, 08 Sep 2021 11:27:10 -0700 (PDT) X-Received: by 2002:a05:6512:34c3:: with SMTP id w3mr3513265lfr.173.1631125630562; Wed, 08 Sep 2021 11:27:10 -0700 (PDT) MIME-Version: 1.0 References: <20210907195226.14b1d22a07c085b22968b933@linux-foundation.org> <20210908025839.81TnA0vU3%akpm@linux-foundation.org> In-Reply-To: <20210908025839.81TnA0vU3%akpm@linux-foundation.org> From: Linus Torvalds Date: Wed, 8 Sep 2021 11:26:54 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [patch 101/147] lib/string: optimized memcpy To: Andrew Morton Cc: David Laight , drew@beagleboard.org, Guo Ren , Christoph Hellwig , kernel@esmil.dk, Linux-MM , mcroce@microsoft.com, mick@ics.forth.gr, mm-commits@vger.kernel.org, Nick Desaulniers , Palmer Dabbelt Content-Type: text/plain; charset="UTF-8" Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=google header.b=eMWgx8GJ; spf=pass (imf13.hostedemail.com: domain of torvalds@linuxfoundation.org designates 209.85.167.45 as permitted sender) smtp.mailfrom=torvalds@linuxfoundation.org; dmarc=none X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 432311029BE0 X-Stat-Signature: 8mapgt7rsg19wsrd4rgspiatzj3pkhxc X-HE-Tag: 1631125634-104853 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: I'm going to skip this one too. On Tue, Sep 7, 2021 at 7:58 PM Andrew Morton wrote: > > From: Matteo Croce > Subject: lib/string: optimized memcpy > > Patch series "lib/string: optimized mem* functions", v2. Honestly, if we change the fallback memcpy(), I think the change should be to remove it. This is a core architecture thing, and every architecture does their own. And pretty much every architecture has their own optimizations for memcpy. Yes, the byte-at-a-time default implementation is bad. But it's _intentionally_ bad. It's only meant for initial bringup. No architecture should actually end up using this in the long run, and if you see it in profiles it should make you go "Ahh" instead. Linus