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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 D350FC432C3 for ; Wed, 27 Nov 2019 19:12:32 +0000 (UTC) Received: from silver.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id AA88A20870 for ; Wed, 27 Nov 2019 19:12:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="dOoHu5Ju" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AA88A20870 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by silver.osuosl.org (Postfix) with ESMTP id 737BC203E5; Wed, 27 Nov 2019 19:12:32 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from silver.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id AmNeLrg7TqyE; Wed, 27 Nov 2019 19:12:31 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by silver.osuosl.org (Postfix) with ESMTP id 7F6B6203D0; Wed, 27 Nov 2019 19:12:31 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 64EF4C1DDA; Wed, 27 Nov 2019 19:12:31 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 5B55AC0881 for ; Wed, 27 Nov 2019 19:12:29 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 4258486F87 for ; Wed, 27 Nov 2019 19:12:29 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id h9FuBiTGe3GT for ; Wed, 27 Nov 2019 19:12:27 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by whitealder.osuosl.org (Postfix) with ESMTPS id 37EA286E88 for ; Wed, 27 Nov 2019 19:12:27 +0000 (UTC) Received: from localhost (unknown [5.29.147.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0161920835; Wed, 27 Nov 2019 19:12:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1574881946; bh=Kf/5NxHVSIFobJHUMSeX3+TDTrwFmhqNDPHnh0UqOdo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=dOoHu5JumTuxbJrzjRT3hV4JQEzObfh08t9Z+gODcqAdZKzTi4Eu2kHYBAqXfytVF nx4i0mymUmYUqUxEpczT4vsroGXuejjIhI9UFlrKBajfdiZ6vo416fak1GdlKtMrhH gHlhrhf3LFVTjSrZaGYZziBl9P1P1NEba5MVXgvk= Date: Wed, 27 Nov 2019 21:12:23 +0200 From: Leon Romanovsky To: Robin Murphy Subject: Re: [PATCH v3 1/7] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions Message-ID: <20191127191223.GF10331@unreal> References: <20191126091946.7970-1-nsaenzjulienne@suse.de> <20191126091946.7970-2-nsaenzjulienne@suse.de> <20191126125137.GA10331@unreal> <6e0b9079-9efd-2884-26d1-3db2d622079d@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Cc: Heiko Stuebner , linux-pci@vger.kernel.org, Shawn Lin , Hanjun Guo , Frank Rowand , Christoph Hellwig , f.fainelli@gmail.com, linux-rockchip@lists.infradead.org, linux-rdma@vger.kernel.org, maz@kernel.org, phil@raspberrypi.org, linux-acpi@vger.kernel.org, Len Brown , devicetree@vger.kernel.org, linux-rpi-kernel@lists.infradead.org, Bjorn Helgaas , linux-arm-kernel@lists.infradead.org, mbrugger@suse.com, netdev@vger.kernel.org, "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, jeremy.linton@arm.com, iommu@lists.linux-foundation.org, Rob Herring , wahrenst@gmx.net, james.quinlan@broadcom.com, Sudeep Holla , "David S. Miller" , Nicolas Saenz Julienne , Tariq Toukan X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Wed, Nov 27, 2019 at 07:06:12PM +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 wrote: > > > > > 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. Create a > > > > > new generic 64bit variant of the function and cleanup rougue custom > > > > > implementations. > > > > > > > > Is it possible to create general roundup/rounddown_pow_two() which will > > > > work correctly for any type of variables, instead of creating special > > > > variant for every type? > > > > > > In fact, that is sort of the case already - roundup_pow_of_two() itself > > > wraps ilog2() such that the constant case *is* type-independent. And > > > since ilog2() handles non-constant values anyway, might it be reasonable > > > to just take the strongly-typed __roundup_pow_of_two() helper out of the > > > loop as below? > > > > > > Robin > > > > > > > That looks way better that's for sure. Some questions. > > > > > ----->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 long n) > > > */ > > > #define roundup_pow_of_two(n) \ > > > ( \ > > > - __builtin_constant_p(n) ? ( \ > > > - (n == 1) ? 1 : \ > > > - (1UL << (ilog2((n) - 1) + 1)) \ > > > - ) : \ > > > - __roundup_pow_of_two(n) \ > > > + (__builtin_constant_p(n) && (n == 1)) ? \ > > > + 1 : (1UL << (ilog2((n) - 1) + 1)) \ > > > > Then here you'd have to use ULL instead of UL, right? I want my 64bit value > > everywhere regardless of the CPU arch. The downside is that would affect > > performance to some extent (i.e. returning a 64bit value where you used to have > > a 32bit one)? > > True, although it's possible that 1ULL might result in the same codegen if > the compiler can see that the result is immediately truncated back to long > anyway. Or at worst, I suppose "(typeof(n))1" could suffice, however ugly. > Either way, this diff was only an illustration rather than a concrete > proposal, but it might be an interesting diversion to investigate. > > On that note, though, you should probably be using ULL in your current patch > too. > > > Also, what about callers to this function on platforms with 32bit 'unsigned > > longs' that happen to input a 64bit value into this. IIUC we'd have a change of > > behaviour. > > Indeed, although the change in such a case would be "start getting the > expected value instead of nonsense", so it might very well be welcome ;) Agree, if code overflowed with 32 bits before this change, the code was already broken. At least now, it won't overflow. > > Robin. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu