linux-kernel - [RFC PATCH 0/2] DMA pagecache

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Date:   Mon, 31 Aug 2020 15:48:57 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Leonardo Bras <leobras.c@...il.com>,
        Joel Stanley <joel@....id.au>,
        Christophe Leroy <christophe.leroy@....fr>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Eric Richter <erichte@...ux.ibm.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Brian King <brking@...ux.vnet.ibm.com>,
        Murilo Fossa Vicentini <muvic@...ux.ibm.com>,
        David Dai <zdai@...ux.vnet.ibm.com>,
        Matthew Wilcox <willy@...radead.org>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 0/2] DMA pagecache

This RFC improves the performance of indirect mapping on all tested DMA
usages, based on a mlx5 device, ranging from 64k packages to 1-byte
packages, from 1 thread to 64 threads.

In all workloads tested, the performance of indirect mapping gets very
near to direct mapping case.

The whole thing is designed to have as much perfomance as possible, so
the impact of the pagecache is not too big.

As I am not very experienced in XArrays usage, nor in lockless
algorithms, I would specially appreaciate feedback on possible
failures on it's usage, missing barriers, and so on.

Also, this size for the FIFO is just for testing purposes.
It's also very possible that it will not be a good idea in platforms
other than pseries, (i have not tested them).
I can plan I bypass for those cases without much work.

Thank you!

Leonardo Bras (2):
  dma-direction: Add DMA_DIR_COMPAT() macro to test direction
    compability
  powerpc/kernel/iommu: Introduce IOMMU DMA pagecache

 arch/powerpc/include/asm/iommu-cache.h |  31 ++++
 arch/powerpc/include/asm/iommu.h       |   4 +
 arch/powerpc/kernel/Makefile           |   2 +-
 arch/powerpc/kernel/iommu-cache.c      | 247 +++++++++++++++++++++++++
 arch/powerpc/kernel/iommu.c            |  15 +-
 include/linux/dma-direction.h          |   3 +
 6 files changed, 296 insertions(+), 6 deletions(-)
 create mode 100644 arch/powerpc/include/asm/iommu-cache.h
 create mode 100644 arch/powerpc/kernel/iommu-cache.c

-- 
2.25.4