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[34.127.87.210]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-39b08ca63b3sm12393723a91.11.2026.09.04.14.40.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Sep 2026 14:40:21 -0700 (PDT) Date: Fri, 4 Sep 2026 21:40:18 +0000 From: Samiullah Khawaja To: David Woodhouse Cc: Lu Baolu , Joerg Roedel , Will Deacon , Jason Gunthorpe , Robin Murphy , Kevin Tian , Alex Williamson , Shuah Khan , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Pratyush Yadav , Pasha Tatashin , David Matlack , Andrew Morton , Pranjal Shrivastava , Vipin Sharma Subject: Re: [PATCH v4 00/18] iommu: Add live update state preservation Message-ID: References: <20260808022723.3893618-1-skhawaja@google.com> <67a636351d656e032bbe64b1ae113821ea4694b7.camel@infradead.org> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <67a636351d656e032bbe64b1ae113821ea4694b7.camel@infradead.org> On Wed, Aug 26, 2026 at 09:12:53AM +0100, David Woodhouse wrote: >On Sat, 2026-08-08 at 02:27 +0000, Samiullah Khawaja wrote: >> This patch series introduces a mechanism for IOMMU state preservation >> across live update, including the Intel VT-d driver support >> implementation. > >Nice work; thanks. Do you have any timing information? Every >millisecond spent on work here is perceived as steal time by the guests >which are paused while it happens. > >So very quickly after the "yay! it works!" stage, we get to the "how do >we do it in <100ms overall steal time" stage... I don't have timing information for this series yet, but I completely agree that every millisecond spent here is perceived as steal time by the guests which are paused while it happens. And this is why we do preservation of the IOMMU state early during LUO preserve() when the guest is not paused. And later LUO freeze(), during shutdown, does the minimum. But we (Google) did some analysis internally on the time for which the guest is paused, and the major time spent in such a kexec liveupdate is in bringing back the rest of the system including important unpreserved devices, other kernel drivers, userspace (VMM) and other major components. Note the Orphaned VMs to reduce the VM pause time: https://lore.kernel.org/all/afEwWZksU0Fw61oT@plex/ Thanks, Sami