Hi Eric, Jean-Philippe
On 2021/4/11 19:12, Eric Auger wrote:
SMMUv3 Nested Stage Setup (IOMMU part)
This series brings the IOMMU part of HW nested paging support
in the SMMUv3. The VFIO part is submitted separately.
This is based on Jean-Philippe's
[PATCH v14 00/10] iommu: I/O page faults for SMMUv3
https://www.spinics.net/lists/arm-kernel/msg886518.html
(including the patches that were not pulled for 5.13)
The IOMMU API is extended to support 2 new API functionalities:
1) pass the guest stage 1 configuration
2) pass stage 1 MSI bindings
Then those capabilities gets implemented in the SMMUv3 driver.
The virtualizer passes information through the VFIO user API
which cascades them to the iommu subsystem. This allows the guest
to own stage 1 tables and context descriptors (so-called PASID
table) while the host owns stage 2 tables and main configuration
structures (STE).
Best Regards
Eric
This series can be found at:
v5.12-rc6-jean-iopf-14-2stage-v15
(including the VFIO part in its last version: v13)
I am testing the performance of an accelerator with/without SVA/vSVA,
and found there might be some potential performance loss risk for SVA/vSVA.
I use a Network and computing encryption device (SEC), and send 1MB
request for 10000 times.
I trigger mm fault before I send the request, so there should be no iopf.
Here's what I got:
physical scenario:
performance: SVA:9MB/s NOSVA:9MB/s
tlb_miss: SVA:302,651 NOSVA:1,223
trans_table_walk_access:SVA:302,276 NOSVA:1,237
VM scenario:
performance: vSVA:9MB/s NOvSVA:6MB/s about 30~40% loss
tlb_miss: vSVA:4,423,897 NOvSVA:1,907
trans_table_walk_access:vSVA:61,928,430 NOvSVA:21,948
In physical scenario, there's almost no performance loss, but the
tlb_miss and trans_table_walk_access of stage 1 for SVA is quite high,
comparing to NOSVA.
In VM scenario, there's about 30~40% performance loss, this is because
the two stage tlb_miss and trans_table_walk_access is even higher, and
impact the performance.
I compare the procedure of building page table of SVA and NOSVA, and
found that NOSVA uses 2MB mapping as far as possible, while SVA uses
only 4KB.
I retest with huge page, and huge page could solve this problem, the
performance of SVA/vSVA is almost the same as NOSVA.
I am wondering do you have any other solution for the performance loss
of vSVA, or any other method to reduce the tlb_miss/trans_table_walk.
Thanks
Xingang
.
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