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Tue, 18 Jul 2023 08:56:39 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1qLn42-002YJT-5I; Tue, 18 Jul 2023 12:56:38 -0300 Date: Tue, 18 Jul 2023 12:56:38 -0300 From: Jason Gunthorpe To: Alex Williamson Cc: Grzegorz Jaszczyk , Christian Brauner , linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-usb@vger.kernel.org, Matthew Rosato , Paul Durrant , Tom Rix , Jason Wang , dri-devel@lists.freedesktop.org, Michal Hocko , linux-mm@kvack.org, Kirti Wankhede , Paolo Bonzini , Jens Axboe , Vineeth Vijayan , Diana Craciun , Alexander Gordeev , Xuan Zhuo , Shakeel Butt , Vasily Gorbik , Leon Romanovsky , Harald Freudenberger , Fei Li , x86@kernel.org, Roman Gushchin , Halil Pasic , Ingo Molnar , intel-gfx@lists.freedesktop.org, Christian Borntraeger , linux-fpga@vger.kernel.org, Zhi Wang , Wu Hao , Jason Herne , Eric Farman , Dave Hansen , Andrew Donnellan , Arnd Bergmann , linux-s390@vger.kernel.org, Heiko Carstens , Johannes Weiner , linuxppc-dev@lists.ozlabs.org, Eric Auger , Borislav Petkov , kvm@vger.kernel.org, Rodrigo Vivi , cgroups@vger.kernel.org, Thomas Gleixner , virtualization@lists.linux-foundation.org, intel-gvt-dev@lists.freedesktop.org, io-uring@vger.kernel.org, netdev@vger.kernel.org, Tony Krowiak , Tvrtko Ursulin , Pavel Begunkov , Sean Christopherson , Oded Gabbay , Muchun Song , Peter Oberparleiter , linux-kernel@vger.kernel.org, linux-rdma@vger.kernel.org, Benjamin LaHaise , "Michael S. Tsirkin" , Sven Schnelle , Greg Kroah-Hartman , Frederic Barrat , Moritz Fischer , Vitaly Kuznetsov , David Woodhouse , Xu Yilun , Dominik Behr , Marcin Wojtas Subject: Re: [PATCH 0/2] eventfd: simplify signal helpers Message-ID: References: <20230630155936.3015595-1-jaz@semihalf.com> <20230714-gauner-unsolidarisch-fc51f96c61e8@brauner> <20230717130831.0f18381a.alex.williamson@redhat.com> <20230717165203.4ee6b1e6.alex.williamson@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230717165203.4ee6b1e6.alex.williamson@redhat.com> X-Rspamd-Queue-Id: 3BF16140009 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: eewchm4b3buzm835gtzejmcyqffxtgea X-HE-Tag: 1689695800-177831 X-HE-Meta: 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 jxJgG2Li dNsjWN1FQdOF3q431w62BsfFBM2qjVpqp2q5CSCQhDUD9slB7gwWKKD1aKnv1omECqfmJRkppfniKMGD3bIQ4ka3dXvfcAST97zODAqr+RAAP/mCKjufvqhtlMTlysQsrLpU+JjXd69Tvwj+ianxak6kO7ibYAZj0NjhgBzKCEYuOA1XW4dJS7jqlJ2IlBM9iFKTiZEJ7JHNoFhjBZCaUPM4aEBKz63alo8jX+ZpBbeXR09rx7We56Fezu0nq8HzOw/uHyRaV8yWJb2TVIc3RfF5jIE/W1mKJgz5JFherbD4XIozblSN1HKaLlnJrUtAQTJZzKllIgFcPXk+BHZtiLqQZO5i7cxm67TTox16nCrnBzmC13NQ6UKAyIM87Cbgq4BP7Zg6q4HiYq4w0GMAPEagWiTBBRH2xoEe3vktCywFdEQjg0exnSxbNvqFhBFXnFQ1w 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: On Mon, Jul 17, 2023 at 04:52:03PM -0600, Alex Williamson wrote: > On Mon, 17 Jul 2023 19:12:16 -0300 > Jason Gunthorpe wrote: > > > On Mon, Jul 17, 2023 at 01:08:31PM -0600, Alex Williamson wrote: > > > > > What would that mechanism be? We've been iterating on getting the > > > serialization and buffering correct, but I don't know of another means > > > that combines the notification with a value, so we'd likely end up with > > > an eventfd only for notification and a separate ring buffer for > > > notification values. > > > > All FDs do this. You just have to make a FD with custom > > file_operations that does what this wants. The uAPI shouldn't be able > > to tell if the FD is backing it with an eventfd or otherwise. Have the > > kernel return the FD instead of accepting it. Follow the basic design > > of eg mlx5vf_save_fops > > Sure, userspace could poll on any fd and read a value from it, but at > that point we're essentially duplicating a lot of what eventfd provides > for a minor(?) semantic difference over how the counter value is > interpreted. Using an actual eventfd allows the ACPI notification to > work as just another interrupt index within the existing vfio IRQ > uAPI. Yes, duplicated, sort of, whatever the "ack" is to allow pushing a new value can be revised to run as part of the read. But I don't really view it as a minor difference. eventfd is a counter. It should not be abused otherwise, even if it can be made to work. It really isn't an IRQ if it is pushing an async message w/data. Jason