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AMD IOMMU v1 is unique in supporting contiguous pages with a variable size
and it can decode the full 64 bit VA space. Unlike other x86 page tables
this explicitly does not do sign extension as part of allowing the entire
64 bit VA space to be supported.
The general design is quite similar to the x86 PAE format, except with a
6th level and quite different PTE encoding.
This format is the only one that uses the PT_FEAT_DYNAMIC_TOP feature in
the existing code as the existing AMDv1 code starts out with a 3 level
table and adds levels on the fly if more IOVA is needed.
Comparing the performance of several operations to the existing version:
iommu_map()
pgsz ,avg new,old ns, min new,old ns , min % (+ve is better)
2^12, 65,64 , 62,61 , -1.01
2^13, 70,66 , 67,62 , -8.08
2^14, 73,69 , 71,65 , -9.09
2^15, 78,75 , 75,71 , -5.05
2^16, 89,89 , 86,84 , -2.02
2^17, 128,121 , 124,112 , -10.10
2^18, 175,175 , 170,163 , -4.04
2^19, 264,306 , 261,279 , 6.06
2^20, 444,525 , 438,489 , 10.10
2^21, 60,62 , 58,59 , 1.01
256*2^12, 381,1833 , 367,1795 , 79.79
256*2^21, 375,1623 , 356,1555 , 77.77
256*2^30, 356,1338 , 349,1277 , 72.72
iommu_unmap()
pgsz ,avg new,old ns, min new,old ns , min % (+ve is better)
2^12, 76,89 , 71,86 , 17.17
2^13, 79,89 , 75,86 , 12.12
2^14, 78,90 , 74,86 , 13.13
2^15, 82,89 , 74,86 , 13.13
2^16, 79,89 , 74,86 , 13.13
2^17, 81,89 , 77,87 , 11.11
2^18, 90,92 , 87,89 , 2.02
2^19, 91,93 , 88,90 , 2.02
2^20, 96,95 , 91,92 , 1.01
2^21, 72,88 , 68,85 , 20.20
256*2^12, 372,6583 , 364,6251 , 94.94
256*2^21, 398,6032 , 392,5758 , 93.93
256*2^30, 396,5665 , 389,5258 , 92.92
The ~5-17x speedup when working with mutli-PTE map/unmaps is because the
AMD implementation rewalks the entire table on every new PTE while this
version retains its position. The same speedup will be seen with dirtys as
well.
The old implementation triggers a compiler optimization that ends up
generating a "rep stos" memset for contiguous PTEs. Since AMD can have
contiguous PTEs that span 2Kbytes of table this is a huge win compared to
a normal movq loop. It is why the unmap side has a fairly flat runtime as
the contiguous PTE sides increases. This version makes it explicit with a
memset64() call.
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Tested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Tested-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.