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[34.143.210.2]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-309ef097e0csm11594174a91.25.2025.04.29.11.57.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Apr 2025 11:57:41 -0700 (PDT) Date: Tue, 29 Apr 2025 18:57:30 +0000 From: Pranjal Shrivastava To: Nicolin Chen Cc: jgg@nvidia.com, kevin.tian@intel.com, corbet@lwn.net, will@kernel.org, bagasdotme@gmail.com, robin.murphy@arm.com, joro@8bytes.org, thierry.reding@gmail.com, vdumpa@nvidia.com, jonathanh@nvidia.com, shuah@kernel.org, jsnitsel@redhat.com, nathan@kernel.org, peterz@infradead.org, yi.l.liu@intel.com, mshavit@google.com, zhangzekun11@huawei.com, iommu@lists.linux.dev, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-tegra@vger.kernel.org, linux-kselftest@vger.kernel.org, patches@lists.linux.dev, mochs@nvidia.com, alok.a.tiwari@oracle.com, vasant.hegde@amd.com Subject: Re: [PATCH v2 10/22] iommufd/viommmu: Add IOMMUFD_CMD_VCMDQ_ALLOC ioctl Message-ID: References: <094992b874190ffdcf6012104b419c8649b5e4b4.1745646960.git.nicolinc@nvidia.com> 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 Content-Disposition: inline In-Reply-To: On Tue, Apr 29, 2025 at 11:15:00AM -0700, Nicolin Chen wrote: > On Tue, Apr 29, 2025 at 06:10:31PM +0000, Pranjal Shrivastava wrote: > > On Tue, Apr 29, 2025 at 08:28:01AM +0000, Pranjal Shrivastava wrote: > > > On Mon, Apr 28, 2025 at 03:44:08PM -0700, Nicolin Chen wrote: > > > > On Mon, Apr 28, 2025 at 09:34:05PM +0000, Pranjal Shrivastava wrote: > > > > > On Fri, Apr 25, 2025 at 10:58:05PM -0700, Nicolin Chen wrote: > > > [...] > > > > > IIUC, one vintf can have multiple lvcmdqs and looking at the series > > > > > it looks like the vcmdq_alloc allocates a single lvcmdq. Is the plan to > > > > > dedicate one lvcmdq to per VM? Which means VMs can share a vintf? > > > > > > > > VINTF is a vSMMU instance per SMMU. Each VINTF can have multiple > > > > LVCMDQs. Each vCMDQ is allocated per IOMMUFD_CMD_VCMDQ_ALLOC. In > > > > other word, VM can issue multiple IOMMUFD_CMD_VCMDQ_ALLOC calls > > > > for each VTINF/vSMMU. > > > > > > > > > > Ack. I'm just wondering why would a single VM want more than one vCMDQ > > > per vSMMU? > > > [...] > > > > I guess the only thing on this patch from me was to understand why > > would a single VM want more than one vCMDQ per vSMMU? (Just curious to > > know :) ) > > It gives some perf gain since it has two portals to fill commands. Ohh! I'm imagining concurrent invalidations / commands! Interesting! > > Nicolin Thanks! Praan