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s=arc-20220608; d=hostedemail.com; t=1745846413; a=rsa-sha256; cv=none; b=mZbKxqZxt9KqbkP/kM48YateS4GvAja4Y3OjfzrgSAtD/pkTavNTb4h06y7l6mdtsDjFB9 mM6onQYV+MRHj4oRn/LJpTSMLg0tFEP/UTPzD4tC9BRKuerJ42X4KoL03ePw7KJF/pz7Dy I6stnkfriwWVNAYvvmfShCIx1WHnAuM= ARC-Authentication-Results: i=1; imf11.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=lst.de; spf=pass (imf11.hostedemail.com: domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de Received: by verein.lst.de (Postfix, from userid 2407) id 3A2B668C4E; Mon, 28 Apr 2025 15:20:06 +0200 (CEST) Date: Mon, 28 Apr 2025 15:20:06 +0200 From: Christoph Hellwig To: Leon Romanovsky Cc: Luis Chamberlain , Marek Szyprowski , Jens Axboe , Christoph Hellwig , Keith Busch , Jake Edge , Jonathan Corbet , Jason Gunthorpe , Zhu Yanjun , Robin Murphy , Joerg Roedel , Will Deacon , Sagi Grimberg , Bjorn Helgaas , Logan Gunthorpe , Yishai Hadas , Shameer Kolothum , Kevin Tian , Alex Williamson , =?iso-8859-1?B?Suly9G1l?= Glisse , Andrew Morton , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-block@vger.kernel.org, linux-rdma@vger.kernel.org, iommu@lists.linux.dev, linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, Niklas Schnelle , Chuck Lever , Matthew Wilcox , Dan Williams , Kanchan Joshi , Chaitanya Kulkarni Subject: Re: [PATCH v9 07/24] dma-mapping: Implement link/unlink ranges API Message-ID: <20250428132006.GA30966@lst.de> References: <2d6ca43ef8d26177d7674b9e3bdf0fe62b55a7ed.1745394536.git.leon@kernel.org> <20250427081312.GE5848@unreal> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250427081312.GE5848@unreal> User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1D6C040007 X-Rspam-User: X-Stat-Signature: m78ppaxz1o39fmfnabjtbgqb5iphgm9i X-HE-Tag: 1745846412-476620 X-HE-Meta: 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 ZU+i2pSZ dl5dNTbG8AHdeXY8iUv80ZNRKUy0qnYSXdIBXBgVdcROgBip13QT6B3zC5wLIw0ED84+lhYYvkH7x4ydB8aOdrj+C94jjCUHHzoghqI+niuOjhfKQ/Ov/DTmR8w== 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: List-Subscribe: List-Unsubscribe: On Sun, Apr 27, 2025 at 11:13:12AM +0300, Leon Romanovsky wrote: > > So arch_sync_dma_for_device() is a no-op on some architectures, notably x86. > > So since you're doing this work and given the above pattern is common on > > the non iova case, we could save ourselves 2 branches checks on x86 on > > __dma_iova_link() and also generalize savings for the non-iova case as > > well. For the non-iova case we have two use cases, one with the attrs on > > initial mapping, and one without on subsequent sync ops. For the iova > > case the attr is always consistently used. > > I want to believe that compiler will discards these "if (!coherent && > !(attrs & DMA_ATTR_SKIP_CPU_SYNC)))" branch if case is empty. Yes, it is the poster child for dead code elimination using the IS_ENABLED() helper. > checks are scattered over all dma-iommu.c file with different > combinations. While we can do new static functions for small number of > use cases, it will be half-solution. Don't bother.