Re: [RFC PATCH v4 00/18] pkeys-based page table hardening

[Ingo Molnar <mingo@kernel.org>]

* Kevin Brodsky <kevin.brodsky@arm.com> wrote:

> Performance
> ===========
> 
> Caveat: these numbers should be seen as a lower bound for the overhead
> of a real POE-based protection. The hardware checks added by POE are
> however not expected to incur significant extra overhead.
> 
> +-------------------+----------------------------------+------------------+---------------+
> | Benchmark         | Result Class                     | Without batching | With batching |
> +===================+==================================+==================+===============+
> | mmtests/kernbench | elsp-64                          |            0.20% |         0.20% |
> |                   | syst-64                          |            1.62% |         0.63% |
> |                   | user-64                          |           -0.04% |         0.05% |
> +-------------------+----------------------------------+------------------+---------------+
> | micromm/fork      | fork: p:1                        |      (R) 225.56% |        -0.07% |
> |                   | fork: p:512                      |      (R) 254.32% |         0.73% |
> +-------------------+----------------------------------+------------------+---------------+
> | micromm/munmap    | munmap: p:1                      |       (R) 24.49% |         4.29% |
> |                   | munmap: p:512                    |      (R) 161.47% |     (R) 6.06% |
> +-------------------+----------------------------------+------------------+---------------+
> | micromm/vmalloc   | fix_size_alloc_test: p:1, h:0    |       (R) 14.80% |    (R) 11.85% |
> |                   | fix_size_alloc_test: p:4, h:0    |       (R) 38.42% |    (R) 10.47% |
> |                   | fix_size_alloc_test: p:16, h:0   |       (R) 64.74% |     (R) 6.41% |
> |                   | fix_size_alloc_test: p:64, h:0   |       (R) 79.98% |     (R) 3.24% |
> |                   | fix_size_alloc_test: p:256, h:0  |       (R) 85.46% |     (R) 2.77% |
> |                   | fix_size_alloc_test: p:16, h:1   |       (R) 47.89% |         3.10% |
> |                   | fix_size_alloc_test: p:64, h:1   |       (R) 62.43% |         3.36% |
> |                   | fix_size_alloc_test: p:256, h:1  |       (R) 64.30% |     (R) 2.68% |
> |                   | random_size_alloc_test: p:1, h:0 |       (R) 74.94% |     (R) 3.13% |
> |                   | vm_map_ram_test: p:1, h:0        |       (R) 30.53% |    (R) 26.20% |
> +-------------------+----------------------------------+------------------+---------------+

So I had to look 3 times to figure out what the numbers mean: they are 
the extra overhead from this hardening feature, measured in system time 
percentage, right?

So "4.29%" means there's a 4.29% slowdown on that particular workload 
when the feature is enabled. Maybe add an explanation to the next iteration? :-)

Thanks,

	Ingo