linux-kernel - Re: [PATCH v5 0/5] iommu: Allow IOVA rcache range be configured

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Date:   Mon, 28 Feb 2022 09:44:19 +0000
From:   John Garry <john.garry@...wei.com>
To:     <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>
CC:     <mst@...hat.com>, <jasowang@...hat.com>,
        <baolu.lu@...ux.intel.com>, <iommu@...ts.linux-foundation.org>,
        <linux-kernel@...r.kernel.org>,
        <virtualization@...ts.linux-foundation.org>, <hch@....de>,
        <chenxiang66@...ilicon.com>, <linuxarm@...wei.com>
Subject: Re: [PATCH v5 0/5] iommu: Allow IOVA rcache range be configured

On 14/02/2022 17:29, John Garry wrote:

Hi guys,

And a friendly reminder on this series also.

Cheers,
john


> For streaming DMA mappings involving an IOMMU and whose IOVA len regularly
> exceeds the IOVA rcache upper limit (meaning that they are not cached),
> performance can be reduced.
> 
> This may be much more pronounced from commit 4e89dce72521 ("iommu/iova:
> Retry from last rb tree node if iova search fails"), as discussed at [0].
> 
> IOVAs which cannot be cached are highly involved in the IOVA ageing issue,
> as discussed at [1].
> 
> This series allows the IOVA rcache range be configured, so that we may
> cache all IOVAs per domain, thus improving performance.
> 
> A new IOMMU group sysfs file is added - max_opt_dma_size - which is used
> indirectly to configure the IOVA rcache range:
> /sys/kernel/iommu_groups/X/max_opt_dma_size
> 
> This file is updated same as how the IOMMU group default domain type is
> updated, i.e. must unbind the only device in the group first.
> 
> The inspiration here comes from block layer request queue sysfs
> "optimal_io_size" file, in /sys/block/sdX/queue/optimal_io_size
> 
> Some old figures* for storage scenario (when increasing IOVA rcache range
> to cover all DMA mapping sizes from the LLD):
> v5.13-rc1 baseline:			1200K IOPS
> With series:				1800K IOPS
> 
> All above are for IOMMU strict mode. Non-strict mode gives ~1800K IOPS in
> all scenarios.
> 
> Based on v5.17-rc4 + [2]
> * I lost my high data throughout test setup
> 
> Differences to v4:
> https://lore.kernel.org/linux-iommu/1626259003-201303-1-git-send-email-john.garry@huawei.com/
> - Major rebase
> - Change the "Refactor iommu_group_store_type()" to not use a callback
>    and an op type enum instead
>    - I didn't pick up Will's Ack as it has changed so much
> - Use a domain feature flag to keep same default group type
> - Add wrapper for default IOVA rcache range
> - Combine last 2x patches
> 
> [0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/
> [1] https://lore.kernel.org/linux-iommu/1607538189-237944-1-git-send-email-john.garry@huawei.com/
> [2] https://lore.kernel.org/linux-iommu/20220203063345-mutt-send-email-mst@kernel.org/T/#m5b2b59576d35cad544314470f32e5f40ac5d1fe9
> 
> John Garry (5):
>    iommu: Refactor iommu_group_store_type()
>    iova: Allow rcache range upper limit to be flexible
>    iommu: Allow iommu_change_dev_def_domain() realloc same default domain
>      type
>    iommu: Allow max opt DMA len be set for a group via sysfs
>    iova: Add iova_len argument to iova_domain_init_rcaches()
> 
>   .../ABI/testing/sysfs-kernel-iommu_groups     |  16 ++
>   drivers/iommu/dma-iommu.c                     |  15 +-
>   drivers/iommu/iommu.c                         | 202 +++++++++++++-----
>   drivers/iommu/iova.c                          |  37 ++--
>   drivers/vdpa/vdpa_user/iova_domain.c          |   4 +-
>   include/linux/iommu.h                         |   7 +
>   include/linux/iova.h                          |   6 +-
>   7 files changed, 212 insertions(+), 75 deletions(-)
>