linux-kernel - Re: [PATCH v2 00/15] dma mapping/iommu: Allow IOMMU IOVA rcache range to be configured

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Date:   Thu, 20 May 2021 09:28:36 +0100
From:   John Garry <john.garry@...wei.com>
To:     <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>,
        <hch@....de>, <m.szyprowski@...sung.com>
CC:     <iommu@...ts.linux-foundation.org>, <baolu.lu@...ux.intel.com>,
        <linux-kernel@...r.kernel.org>, <linux-scsi@...r.kernel.org>,
        <linuxarm@...wei.com>
Subject: Re: [PATCH v2 00/15] dma mapping/iommu: Allow IOMMU IOVA rcache range
 to be configured

On 10/05/2021 15:17, John Garry wrote:

Hi Robin, guys,

A friendly reminder on this one...

Thanks

> 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 is 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 aging 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. However, the
> IOMMU default domain is reallocated in the device driver reprobe, and not
> immediately.
> 
> In addition, we keep (from v1 series) the DMA mapping API to allow DMA max
> optimised size be set from a LLDD. How it works is a lot different. When
> the LLDD calls this during probe, once the value is successfully recorded, we
> return -EDEFER_PROBE. In the reprobe, the IOMM group default domain is
> reallocated, and the new IOVA domain rcache upper limit is set according
> to that DMA max optimised size. As such, we don't operate on a live IOMMU
> domain.
> 
> Note that the DMA mapping API frontend is not strictly required, but saves
> the LLDD calling IOMMU APIs directly, that being not preferred.
> 
> Some figures for storage scenario:
> 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.
> 
> Patch breakdown:
> 1-11: Add support for setting DMA max optimised size via sysfs
> 12-15: Add support for setting DMA max optimised size from LLDD
> 
> [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/
> 
> Differences to v1:
> - Many
> - Change method to not operate on a 'live' IOMMU domain:
> 	- rather, force device driver to be re-probed once
> 	  dma_max_opt_size is set, and reconfig a new IOMMU group then
> - Add iommu sysfs max_dma_opt_size file, and allow updating same as how
>    group type is changed
> 
> John Garry (15):
>    iommu: Reactor iommu_group_store_type()
>    iova: Allow rcache range upper limit to be flexible
>    iommu: Allow max opt DMA len be set for a group via sysfs
>    iommu: Add iommu_group_get_max_opt_dma_size()
>    iova: Add iova_domain_len_is_cached()
>    iommu: Allow iommu_change_dev_def_domain() realloc default domain for
>      same type
>    iommu: Add iommu_realloc_dev_group()
>    dma-iommu: Add iommu_reconfig_dev_group_dma()
>    iova: Add init_iova_domain_ext()
>    dma-iommu: Use init_iova_domain_ext() for IOVA domain init
>    dma-iommu: Reconfig group domain
>    iommu: Add iommu_set_dev_dma_opt_size()
>    dma-mapping: Add dma_set_max_opt_size()
>    dma-iommu: Add iommu_dma_set_opt_size()
>    scsi: hisi_sas: Set max optimal DMA size for v3 hw
> 
>   drivers/iommu/dma-iommu.c              |  51 +++++-
>   drivers/iommu/iommu.c                  | 231 +++++++++++++++++++------
>   drivers/iommu/iova.c                   |  61 +++++--
>   drivers/scsi/hisi_sas/hisi_sas_v3_hw.c |   5 +
>   include/linux/dma-iommu.h              |   4 +
>   include/linux/dma-map-ops.h            |   1 +
>   include/linux/dma-mapping.h            |   8 +
>   include/linux/iommu.h                  |  19 ++
>   include/linux/iova.h                   |  21 ++-
>   kernel/dma/mapping.c                   |  11 ++
>   10 files changed, 344 insertions(+), 68 deletions(-)
>