[PATCH v2 4/8] dma-mapping: Separate DMA sync issuing and completion waiting

[Jürgen Groß]

On 26.12.25 23:52, Barry Song wrote:
> From: Barry Song <baohua at kernel.org>
> 
> Currently, arch_sync_dma_for_cpu and arch_sync_dma_for_device
> always wait for the completion of each DMA buffer. That is,
> issuing the DMA sync and waiting for completion is done in a
> single API call.
> 
> For scatter-gather lists with multiple entries, this means
> issuing and waiting is repeated for each entry, which can hurt
> performance. Architectures like ARM64 may be able to issue all
> DMA sync operations for all entries first and then wait for
> completion together.
> 
> To address this, arch_sync_dma_for_* now issues DMA operations in
> batch, followed by a flush. On ARM64, the flush is implemented
> using a dsb instruction within arch_sync_dma_flush().
> 
> For now, add arch_sync_dma_flush() after each
> arch_sync_dma_for_*() call. arch_sync_dma_flush() is defined as a
> no-op on all architectures except arm64, so this patch does not
> change existing behavior. Subsequent patches will introduce true
> batching for SG DMA buffers.
> 
> Cc: Leon Romanovsky <leon at kernel.org>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Cc: Marek Szyprowski <m.szyprowski at samsung.com>
> Cc: Robin Murphy <robin.murphy at arm.com>
> Cc: Ada Couprie Diaz <ada.coupriediaz at arm.com>
> Cc: Ard Biesheuvel <ardb at kernel.org>
> Cc: Marc Zyngier <maz at kernel.org>
> Cc: Anshuman Khandual <anshuman.khandual at arm.com>
> Cc: Ryan Roberts <ryan.roberts at arm.com>
> Cc: Suren Baghdasaryan <surenb at google.com>
> Cc: Joerg Roedel <joro at 8bytes.org>
> Cc: Juergen Gross <jgross at suse.com>
> Cc: Stefano Stabellini <sstabellini at kernel.org>
> Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko at epam.com>
> Cc: Tangquan Zheng <zhengtangquan at oppo.com>
> Signed-off-by: Barry Song <baohua at kernel.org>

Reviewed-by: Juergen Gross <jgross at suse.com> # drivers/xen/swiotlb-xen.c


Juergen
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