IOMMU: avoid lock contention in iova allocation

Hi,

iova alloc/free causes big lock contention, which could be easily demonstrated with iperf workload. Previously I posted a patchset:
http://lists.linuxfoundation.org/pipermail/iommu/2015-November/014984.html

the concern is it's not generic. This is another try for the issue. This version implements a per-cpu iova cache for small size DMA allocation (<= 64k), which should be generic enough and so we can do batch allocation. iova free could be easily batched too. With batch alloc/free, iova lock contention disappears. Performance result with this patchset is nearly the same as the previous one in the same test.

After this patchset, async_umap_flush_lock becomes the hotest lock in intel-iommu, but not very bad. That will be something we need work on in the future.

Thanks,
Shaohua

Shaohua Li (4):
IOMMU: add a percpu cache for iova allocation
iommu: free_iova doesn't need lock twice
intel-iommu: remove find_iova in unmap path
intel-iommu: do batch iova free

 drivers/iommu/intel-iommu.c |  77 +++++++++++++------
 drivers/iommu/iova.c        | 177 +++++++++++++++++++++++++++++++++++---------
 include/linux/iova.h        |  10 +++
 3 files changed, 208 insertions(+), 56 deletions(-)

2.4.6