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 v5.18-rc1 * I lost my high data throughout test setup Differences to v4: https://lore.kernel.org/linux-iommu/1626259003-201303-1-git-send-email-john.ga...@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.leiz...@huawei.com/ [1] https://lore.kernel.org/linux-iommu/1607538189-237944-1-git-send-email-john.ga...@huawei.com/ 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(-) -- 2.26.2 _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu