[PATCH v1 0/3] swiotlb performance optimizations

[Chao Gao]

Intent of this post:
 Seek reviews from Intel reviewers and anyone else in the list
 interested in IO performance in confidential VMs. Need some acked-by
 reviewed-by tags before I can add swiotlb maintainers to "to/cc" lists
 and ask for a review from them.

swiotlb is now widely used by confidential VMs. This series optimizes
swiotlb to reduce cache misses and lock contention during bounce buffer
allocation/free and memory bouncing to improve IO workload performance in
confidential VMs.

Here are some FIO tests we did to demonstrate the improvement.

Test setup
----------

A normal VM with 8vCPU and 32G memory, swiotlb is enabled by swiotlb=force.
100 in Host/Guest CPU utilization means 1 logical processor. FIO block size
is 4K and iodepth is 256. Note that a normal VM is used so that others lack
of necessary hardware to host confidential VMs can reproduce results below.

Results
-------

1 FIO job	read/write	Throughput	IOPS	Host CPU	Guest CPU
				(MB/s)		(k)	utilization	utilization
vanilla		read		1037		253	228.48		101.92
		write		1148		280	233.28		100.96
optimized	read		1160		283	232.32		101.12
		write		1195		292	233.28		100.64

1-job FIO sequential read/write perf increase by 12% and 4% respectively.

4 FIO jobs	read/write	Throughput	IOPS	Host CPU	Guest CPU
				(MB/s)		(k)	utilization	utilization
vanilla		read		885		214.9	527.04		401.12
		write		868		212.1	531.84		400.64
optimized	read		2320		567	344.64		202.8
		write		1998		488	312		173.92

4-job FIO sequential read/write perf increase by 164% and 130% respectively.

This series is based on 5.19-rc2.

Andi Kleen (1):
  swiotlb: Split up single swiotlb lock

Chao Gao (2):
  swiotlb: Use bitmap to track free slots
  swiotlb: Allocate memory in a cache-friendly way

 .../admin-guide/kernel-parameters.txt         |   4 +-
 arch/x86/kernel/acpi/boot.c                   |   4 +
 include/linux/swiotlb.h                       |  47 +++-
 kernel/dma/swiotlb.c                          | 263 +++++++++++++-----
 4 files changed, 229 insertions(+), 89 deletions(-)

-- 
2.25.1