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Subject[PATCH v1 0/3] swiotlb performance optimizations
Date
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

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