Re: [PATCH v3 next 06/13] kallsyms: Improve selftest test_perf_kallsyms_lookup_name() output

[bot+bpf-ci@kernel.org]

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> kallsyms: Improve selftest test_perf_kallsyms_lookup_name() output

TL;DR: Commit message only: it says 4 functions get noinline_for_stack but the
patch marks 5, and it omits the compression-ratio output format fix; maybe
split that into a separate patch.

> kallsyms: Improve selftest test_perf_kallsyms_lookup_name() output
>
> - Improve the test stability/reproducability by taking the faster of
>   two calls to kallsyms_lookup_name().
> - Check that kallsyms_lookup_name() returns the expected address
>   unless the symbol is duplicated.
> - Report the names of the min/max symbols.
> - Output an 8 line 64 entry histogram of the times taken.
> - This shows there is a reasonably normal distribution with a small
>   number of much slower outliers that don't really affect the average.
>
> Additionally:
> - Add a very long symbol to check the handling of two byte lengths.
> - Do the test_perf_kallsyms_lookup_name() last because it can take long
>   enough that the CPU frequency changes and the times reported by the
>   other tests can change.
> - Mark the 4 test functions noinline_for_stack since they all have a
>   quite large on-stack structure.
>
> Example output (after all these patches)
> kallsyms_on_each_symbol() traverse all: 7742950 ns
> kallsyms_on_each_match_symbol() traverse all: 951 ns
> kallsyms_lookup_name() looked up 123312 symbols, average 200 ns
>         fastest 60 ns (_rs.0)
>         slowest 662 ns (The_time_has_come_the_Walrus_said_To_talk_of_many_things_Of_sho)
>         Distribution, 20ns per column, 2916 counts per *:
>         |         **
>         |        ****
>         |        ****
>         |        ****
>         |       ******
>         |       *******
>         |      *********
>         |   ******************  **    * * *
>
> Signed-off-by: David Laight <david.laight.linux@gmail.com>
>

The changelog says 4 test functions are marked noinline_for_stack "since they
all have a quite large on-stack structure", but the patch marks five:
test_kallsyms_compression_ratio(), test_perf_kallsyms_lookup_name(),
test_perf_kallsyms_on_each_symbol(), test_perf_kallsyms_on_each_match_symbol()
and test_kallsyms_basic_function().

test_kallsyms_compression_ratio() has only seven u32 locals and no large
on-stack structure, so the stated reason does not cover it.

The same function also changes its output format from "%2d.%-2d" to
"%2d.%02d", which fixes how the fractional part is printed (12.05 used to show
as "12.5 "). The changelog does not mention this.

Could the changelog give the right count and mention the format fix, or should
the compression-ratio changes go in a separate patch?


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