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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 4C6BEC432C0 for ; Wed, 27 Nov 2019 19:16:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2ECD320835 for ; Wed, 27 Nov 2019 19:16:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727007AbfK0TQk (ORCPT ); Wed, 27 Nov 2019 14:16:40 -0500 Received: from mx2.suse.de ([195.135.220.15]:34596 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726593AbfK0TQk (ORCPT ); Wed, 27 Nov 2019 14:16:40 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C825BACEF; Wed, 27 Nov 2019 19:16:36 +0000 (UTC) Message-ID: Subject: Re: [PATCH v3 1/7] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions From: Nicolas Saenz Julienne To: Robin Murphy , Leon Romanovsky Cc: andrew.murray@arm.com, maz@kernel.org, linux-kernel@vger.kernel.org, Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Tariq Toukan , Rob Herring , Frank Rowand , Shawn Lin , Heiko Stuebner , Christoph Hellwig , Marek Szyprowski , james.quinlan@broadcom.com, mbrugger@suse.com, f.fainelli@gmail.com, phil@raspberrypi.org, wahrenst@gmx.net, jeremy.linton@arm.com, linux-pci@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, "Rafael J. Wysocki" , Len Brown , "David S. Miller" , Bjorn Helgaas , linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, devicetree@vger.kernel.org, linux-rockchip@lists.infradead.org, iommu@lists.linux-foundation.org Date: Wed, 27 Nov 2019 20:16:27 +0100 In-Reply-To: References: <20191126091946.7970-1-nsaenzjulienne@suse.de> <20191126091946.7970-2-nsaenzjulienne@suse.de> <20191126125137.GA10331@unreal> <6e0b9079-9efd-2884-26d1-3db2d622079d@arm.com> Content-Type: multipart/signed; micalg="pgp-sha256"; protocol="application/pgp-signature"; boundary="=-O+wgk4AZ6l++1CDkyqmb" User-Agent: Evolution 3.34.1 MIME-Version: 1.0 Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org --=-O+wgk4AZ6l++1CDkyqmb Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2019-11-27 at 19:06 +0000, Robin Murphy wrote: > On 27/11/2019 6:24 pm, Nicolas Saenz Julienne wrote: > > On Wed, 2019-11-27 at 18:06 +0000, Robin Murphy wrote: > > > On 26/11/2019 12:51 pm, Leon Romanovsky wrote: > > > > On Tue, Nov 26, 2019 at 10:19:39AM +0100, Nicolas Saenz Julienne wr= ote: > > > > > Some users need to make sure their rounding function accepts and > > > > > returns > > > > > 64bit long variables regardless of the architecture. Sadly > > > > > roundup/rounddown_pow_two() takes and returns unsigned longs. Cre= ate a > > > > > new generic 64bit variant of the function and cleanup rougue cust= om > > > > > implementations. > > > >=20 > > > > Is it possible to create general roundup/rounddown_pow_two() which = will > > > > work correctly for any type of variables, instead of creating speci= al > > > > variant for every type? > > >=20 > > > In fact, that is sort of the case already - roundup_pow_of_two() itse= lf > > > wraps ilog2() such that the constant case *is* type-independent. And > > > since ilog2() handles non-constant values anyway, might it be reasona= ble > > > to just take the strongly-typed __roundup_pow_of_two() helper out of = the > > > loop as below? > > >=20 > > > Robin > > >=20 > >=20 > > That looks way better that's for sure. Some questions. > >=20 > > > ----->8----- > > > diff --git a/include/linux/log2.h b/include/linux/log2.h > > > index 83a4a3ca3e8a..e825f8a6e8b5 100644 > > > --- a/include/linux/log2.h > > > +++ b/include/linux/log2.h > > > @@ -172,11 +172,8 @@ unsigned long __rounddown_pow_of_two(unsigned lo= ng n) > > > */ > > > #define roundup_pow_of_two(n) \ > > > ( \ > > > - __builtin_constant_p(n) ? ( \ > > > - (n =3D=3D 1) ? 1 : \ > > > - (1UL << (ilog2((n) - 1) + 1)) \ > > > - ) : \ > > > - __roundup_pow_of_two(n) \ > > > + (__builtin_constant_p(n) && (n =3D=3D 1)) ? \ > > > + 1 : (1UL << (ilog2((n) - 1) + 1)) \ > >=20 > > Then here you'd have to use ULL instead of UL, right? I want my 64bit v= alue > > everywhere regardless of the CPU arch. The downside is that would affec= t > > performance to some extent (i.e. returning a 64bit value where you used= to > > have > > a 32bit one)? >=20 > True, although it's possible that 1ULL might result in the same codegen= =20 > if the compiler can see that the result is immediately truncated back to= =20 > long anyway. Or at worst, I suppose "(typeof(n))1" could suffice,=20 > however ugly. Either way, this diff was only an illustration rather than= =20 > a concrete proposal, but it might be an interesting diversion to=20 > investigate. >=20 > On that note, though, you should probably be using ULL in your current= =20 > patch too. I actually meant to, the fix got lost. Thanks for pointing it out. As I see Leon also likes this, I'll try out this implementation and come ba= ck with some results. Regards, Nicolas --=-O+wgk4AZ6l++1CDkyqmb Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- iQEzBAABCAAdFiEErOkkGDHCg2EbPcGjlfZmHno8x/4FAl3ey4sACgkQlfZmHno8 x/4qGggAi4+Q7jM0+bmigNE35y3GihyLXM3ahA2qmQ9ftiZshh+Z8XQUYcRi7852 LsPNmYpHjwV3LyoaBXdnHaIVR5I1rE6RXSAZEK4xRF872qqm9rKDeMGF1GXxrw3u BJl/LR2xhGkhYepUUAiZ+vGy3FyTfl8ADH/V9AHtFtvXuFTpStBZS3/xYgaO9mRa E0hCB01yKy14h+FAXRiEB0E6onkyAqWjLHPmAXCGmk4ZsJwAjdVr3QyVq6AUBBKt CaBQ7gUU8NOTg8ZE9WDRdTfIlQ+1Gpiu2xk1jML8Y1eCGxB3wtXy0t5GdjOaiwzi fzp73AN5N4UigGnR/sl3LgJQXPe3yA== =ixwn -----END PGP SIGNATURE----- --=-O+wgk4AZ6l++1CDkyqmb--