From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yb1-f179.google.com (mail-yb1-f179.google.com [209.85.219.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 88C4535CEA1 for ; Thu, 21 Aug 2025 20:40:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.219.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755808831; cv=none; b=HMATbiWUYlmC1KRmcsKGWTYN92SfvXCaRENj8yN7usKBjKw+fj2Sn1JdUYjQnevYlcjWqsKAWPv8yjXIREKL1ITkTveERlrVUXOp2+9N87UPKV35M3I1dN6lZksLC7RRFgJN+54vZ7fkO9VpbaIse27RBdYd9AYoRgZVdQgIDWY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1755808831; c=relaxed/simple; bh=1qrCIxXCctxTGv3WrCi51BAahcEwkBdshUsK554eypo=; h=MIME-Version:References:In-Reply-To:From:Date:Message-ID:Subject: To:Cc:Content-Type; b=Ll+Mn3H/GUbb1T4/bk3v29Req8JB+kVLi0j+wCnipoHaNYt6Vz7kak9DZA7ma6kWUWDy2R6jg6qtLcaetTWsRKbIgSusx8ny5rlrvbacuaKZ/IrZWSskOxLCiaog3zhuNZkm6T2lzu+VKD/NO32JGN9ZK7bjaILo2wTGCNJGHTM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org; spf=pass smtp.mailfrom=linuxfoundation.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=Xj3eWnKy; arc=none smtp.client-ip=209.85.219.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linuxfoundation.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="Xj3eWnKy" Received: by mail-yb1-f179.google.com with SMTP id 3f1490d57ef6-e932ded97easo1395869276.1 for ; Thu, 21 Aug 2025 13:40:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; t=1755808826; x=1756413626; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=lHa4LrampbSXQx1Wyi9Bh9OjrywcR0PvG9lus2xsnNw=; b=Xj3eWnKyDim2sWrPyXl0eiBk1OWSgs1ksQYyz2QefBrBdLLLXnht5zVD4ZioqosLXN Dz19HC+4B2jldL4kkms2feJWTaQaDtE19/QczTKaZSvVvxdjVQfHCUywxEH8NFqilrQd 0w4Bkj7aKkm66WdkH1tFOjeZ3wgq4J/tQimS0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1755808826; x=1756413626; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=lHa4LrampbSXQx1Wyi9Bh9OjrywcR0PvG9lus2xsnNw=; b=GKxft7d95MDLbr41Bv9taLE0qU5x0eaShcOfwzvU0zYrKSfg1wXCSYy0+fmDgJFsu3 4MwG1/Km637L0wzCvPIjO8laFm5N0ngDCu9yK7RNEsC+5B4I/UKSxh3S+IWA15cGcYN5 Ay7s9BKuJvwe+pDtZ2MiyZryCMUQYyGnc9/trfFcU1gtR0JN6covIw7vLWBJyIOd4mrQ jGMbN4kPEf2R9i+K8OhxRTBMVoL2RqOuujSqeKQPV3EzQOYNKZh+Q5GWbFeuxvqIEFXo lTklwmgxHiAkfBhfvXZ+vbbVDT50RnkM2kXqiSr2iTTQJh6rat0ioEnzibjZjfW8GPgo tHhA== X-Forwarded-Encrypted: i=1; AJvYcCWdbLzI81IRjuCVgQmFovQa+P3QAYt8uBBFyXk5zuEp5zQHUD6S39N+VOZ2v652ciPclpolbmvYQu0=@vger.kernel.org X-Gm-Message-State: AOJu0YwuhRt4v9n0JdrvCvcb50xlXYEBcYCqJPszoaOyfMxoIfeZU00C 3tXtXmIFUd1LTk20DNuc0zSnlScwxEroG/gcNnYx4ulbX5tqevXj5LrFR+GOJKQA4Fk3lf8h8nX kR8pX93O6xfZZkf0YyEa/83j4FvRrN/dFpmL2R0NHcw== X-Gm-Gg: ASbGncvIYwyrR1iCum3xLqv60Z8NniHSQ5IRGMhEG6cZrwmACqkXr6JR2PK/xL6brb2 ZZv951ErXLiv2aW9/u86uWBPkGbD/8rYklUY1ujk+9ev9lWiVZNQc96vkd0FjBkKPaaapUlyyRU hTlATjd2vzTjAzG1WQF0V52je9v8gmVVw9Lv6LJ0q6Z0wP7NtB9uFRDx6TzHg8xHxyPVmTJoU1D W4mlqSKp6+0wQd6 X-Google-Smtp-Source: AGHT+IEDbX/Imr3oMuC/SvPpVgA4gK54+Q+BCEwHjysz7tgNECdpdXbU462KLrYXAP4tYmTYkQFLOtkp14xdKE7/w+U= X-Received: by 2002:a05:6902:c12:b0:e93:457a:37b0 with SMTP id 3f1490d57ef6-e951c33ee1bmr998901276.20.1755808826442; Thu, 21 Aug 2025 13:40:26 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-ide@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250821200701.1329277-1-david@redhat.com> <20250821200701.1329277-32-david@redhat.com> <2926d7d9-b44e-40c0-b05d-8c42e99c511d@redhat.com> In-Reply-To: <2926d7d9-b44e-40c0-b05d-8c42e99c511d@redhat.com> From: Linus Torvalds Date: Thu, 21 Aug 2025 16:40:13 -0400 X-Gm-Features: Ac12FXw_AatpwCNNPCEiMwiwdQxQbayKDzVf5K7yc3iQ5tLY7APrv3zl2U8Z_SA Message-ID: Subject: Re: [PATCH RFC 31/35] crypto: remove nth_page() usage within SG entry To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, Herbert Xu , "David S. Miller" , Alexander Potapenko , Andrew Morton , Brendan Jackman , Christoph Lameter , Dennis Zhou , Dmitry Vyukov , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, iommu@lists.linux.dev, io-uring@vger.kernel.org, Jason Gunthorpe , Jens Axboe , Johannes Weiner , John Hubbard , kasan-dev@googlegroups.com, kvm@vger.kernel.org, "Liam R. Howlett" , linux-arm-kernel@axis.com, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-ide@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mips@vger.kernel.org, linux-mmc@vger.kernel.org, linux-mm@kvack.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, Lorenzo Stoakes , Marco Elver , Marek Szyprowski , Michal Hocko , Mike Rapoport , Muchun Song , netdev@vger.kernel.org, Oscar Salvador , Peter Xu , Robin Murphy , Suren Baghdasaryan , Tejun Heo , virtualization@lists.linux.dev, Vlastimil Babka , wireguard@lists.zx2c4.com, x86@kernel.org, Zi Yan Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, Aug 21, 2025 at 4:29=E2=80=AFPM David Hildenbrand wrote: > > Because doing a 64-bit shift on x86-32 is like three cycles. Doing a > > 64-bit signed division by a simple constant is something like ten > > strange instructions even if the end result is only 32-bit. > > I would have thought that the compiler is smart enough to optimize that? > PAGE_SIZE is a constant. Oh, the compiler optimizes things. But dividing a 64-bit signed value with a constant is still quite complicated. It doesn't generate a 'div' instruction, but it generates something like th= is: movl %ebx, %edx sarl $31, %edx movl %edx, %eax xorl %edx, %edx andl $4095, %eax addl %ecx, %eax adcl %ebx, %edx and that's certainly a lot faster than an actual 64-bit divide would be. An unsigned divide - or a shift - results in just shrdl $12, %ecx, %eax which is still not the fastest instruction (I think shrld gets split into two uops), but it's certainly simpler and easier to read. Linus