linux-kernel - [RFC PATCH 0/5] dma-mapping: arm64: support batched cache sync

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Message-Id: <20251029023115.22809-1-21cnbao@gmail.com>
Date: Wed, 29 Oct 2025 10:31:10 +0800
From: Barry Song <21cnbao@...il.com>
To: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Robin Murphy <robin.murphy@....com>
Cc: Barry Song <v-songbaohua@...o.com>,
	Ada Couprie Diaz <ada.coupriediaz@....com>,
	Ard Biesheuvel <ardb@...nel.org>,
	Marc Zyngier <maz@...nel.org>,
	Anshuman Khandual <anshuman.khandual@....com>,
	Ryan Roberts <ryan.roberts@....com>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Tangquan Zheng <zhengtangquan@...o.com>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Subject: [RFC PATCH 0/5] dma-mapping: arm64: support batched cache sync

From: Barry Song <v-songbaohua@...o.com>

Many embedded ARM64 SoCs still lack hardware cache coherency support, which
causes DMA mapping operations to appear as hotspots in on-CPU flame graphs.

For an SG list with *nents* entries, the current dma_map/unmap_sg() and DMA
sync APIs perform cache maintenance one entry at a time. After each entry,
the implementation synchronously waits for the corresponding region’s
D-cache operations to complete. On architectures like arm64, efficiency can
be improved by issuing all entries’ operations first and then performing a
single batched wait for completion.

Tangquan's initial results show that batched synchronization can reduce
dma_map_sg() time by 64.61% and dma_unmap_sg() time by 66.60% on an MTK
phone platform (MediaTek Dimensity 9500). The tests were performed by
pinning the task to CPU7 and fixing the CPU frequency at 2.6 GHz,
running dma_map_sg() and dma_unmap_sg() on 10 MB buffers (10 MB / 4 KB
sg entries per buffer) for 200 iterations and then averaging the
results.

Barry Song (5):
  arm64: Provide dcache_by_myline_op_nosync helper
  arm64: Provide dcache_clean_poc_nosync helper
  arm64: Provide dcache_inval_poc_nosync helper
  arm64: Provide arch_sync_dma_ batched helpers
  dma-mapping: Allow batched DMA sync operations if supported by the
    arch

 arch/arm64/Kconfig                  |  1 +
 arch/arm64/include/asm/assembler.h  | 79 +++++++++++++++++++-------
 arch/arm64/include/asm/cacheflush.h |  2 +
 arch/arm64/mm/cache.S               | 58 +++++++++++++++----
 arch/arm64/mm/dma-mapping.c         | 24 ++++++++
 include/linux/dma-map-ops.h         |  8 +++
 kernel/dma/Kconfig                  |  3 +
 kernel/dma/direct.c                 | 53 ++++++++++++++++--
 kernel/dma/direct.h                 | 86 +++++++++++++++++++++++++----
 9 files changed, 267 insertions(+), 47 deletions(-)

Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will@...nel.org>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Robin Murphy <robin.murphy@....com>
Cc: Ada Couprie Diaz <ada.coupriediaz@....com>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Anshuman Khandual <anshuman.khandual@....com>
Cc: Ryan Roberts <ryan.roberts@....com>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Tangquan Zheng <zhengtangquan@...o.com>
Cc: linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Cc: iommu@...ts.linux.dev

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