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Mon, 21 Apr 2025 09:17:34 -0700 (PDT) X-Relaying-Domain: purestorage.com Received: from dev-csander.dev.purestorage.com (dev-csander.dev.purestorage.com [10.7.70.37]) by c7-smtp-2023.dev.purestorage.com (Postfix) with ESMTP id 0A8D53402B2; Mon, 21 Apr 2025 10:17:34 -0600 (MDT) Received: by dev-csander.dev.purestorage.com (Postfix, from userid 1557716354) id 04724E41856; Mon, 21 Apr 2025 10:17:34 -0600 (MDT) From: Caleb Sander Mateos To: Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg Cc: Kanchan Joshi , linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, Caleb Sander Mateos Subject: [PATCH v2 0/2] nvme/pci: PRP list DMA pool partitioning Date: Mon, 21 Apr 2025 10:17:23 -0600 Message-ID: <20250421161725.1610286-1-csander@purestorage.com> X-Mailer: git-send-email 2.45.2 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit NVMe commands with more than 4 KB of data allocate PRP list pages from the per-nvme_device dma_pool prp_page_pool or prp_small_pool. Each call to dma_pool_alloc() and dma_pool_free() takes the per-dma_pool spinlock. These device-global spinlocks are a significant source of contention when many CPUs are submitting to the same NVMe devices. On a workload issuing 32 KB reads from 16 CPUs (8 hypertwin pairs) across 2 NUMA nodes to 23 NVMe devices, we observed 2.4% of CPU time spent in _raw_spin_lock_irqsave called from dma_pool_alloc and dma_pool_free. Ideally, the dma_pools would be per-hctx to minimize contention. But that could impose considerable resource costs in a system with many NVMe devices and CPUs. As a compromise, allocate per-NUMA-node PRP list DMA pools. Map each nvme_queue to the set of DMA pools corresponding to its device and its hctx's NUMA node. This reduces the _raw_spin_lock_irqsave overhead by about half, to 1.2%. Preventing the sharing of PRP list pages across NUMA nodes also makes them cheaper to initialize. Caleb Sander Mateos (2): nvme/pci: factor out nvme_init_hctx() helper nvme/pci: make PRP list DMA pools per-NUMA-node drivers/nvme/host/pci.c | 172 +++++++++++++++++++++++----------------- 1 file changed, 99 insertions(+), 73 deletions(-) v2: - Initialize admin nvme_queue's nvme_prp_dma_pools (Kanchan) - Shrink nvme_dev's prp_pools array from MAX_NUMNODES to nr_node_ids (Kanchan) -- 2.45.2