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[34.124.234.44]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c8575db0c37sm2454a12.31.2026.05.28.14.46.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 May 2026 14:46:39 -0700 (PDT) Date: Thu, 28 May 2026 21:46:33 +0000 From: Pranjal Shrivastava To: Nicolin Chen Cc: iommu@lists.linux.dev, Will Deacon , Joerg Roedel , Robin Murphy , Jason Gunthorpe , Mostafa Saleh , Daniel Mentz , Ashish Mhetre , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v7 10/11] iommu/arm-smmu-v3: Invoke pm_runtime before hw access Message-ID: References: <20260527221407.1756491-1-praan@google.com> <20260527221407.1756491-11-praan@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260528_144641_152221_B0F55282 X-CRM114-Status: GOOD ( 12.50 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, May 28, 2026 at 01:28:15PM -0700, Nicolin Chen wrote: > On Wed, May 27, 2026 at 10:14:06PM +0000, Pranjal Shrivastava wrote: > > TLB and CFG invalidations are > > elided if the SMMU is suspended by observing the CMDQ_PROD_STOP_FLAG via > > the arm_smmu_can_elide() helper. > > All the arm_smmu_can_elide() call sites here would eventually elide > the commands in arm_smmu_cmdq_issue_cmdlist() that is already gated > by CMDQ_PROD_STOP_FLAG? It doesn't seem necessary to gate again? While issue_cmdlist() would eventually elide these commands, the can_elide() check is necessary to return early during suspension. This avoids unnecessary stack allocation, cmd building, and spinlock contention on the cmdq->lock for threads that are anyway about to be elided. By dropping these requests immediately, we significantly reduce cacheline bouncing and contention during unmap storms. Furthermore, the early check also allows us to specifically trigger the WARN_ON_ONCE() for broken devlinks. Thanks, Praan