Shulou(Shulou.com)11/24 Report--

CTOnews.com reported on December 14 that Linux 6.2 today incorporated code from Huawei Zheng Lei (Zhen Lei), increasing the speed of core kernel functions 715 times.

In the introduction to the merge code module, it is written: "thanks to the code of Zhen Lei, Tux (the mascot of Linux, which means Linux) has improved its average lookup performance at kallsyms_lookup_name () by 715 times, upgrading our old implementation from O (n) to O (log (n)) while retaining the old implementation support on / proc / kallsyms."

CTOnews.com learned that the kallsyms_lookup_name () function is used to query the address of a symbol based on its name and can be used to query any symbol in the kernel symbol table.

Huawei's Zhen Lei described the optimization of kallsyms_lookup_name in a previous patch:

Currently, to search for a symbol, we need to expand the symbols in 'kallsyms_names' one by one, and then compare them using the expanded string. This is O (n).

If we sort names in ascending order like addresses, we can also use binary search. And this is O (log (n)).

In order not to change the implementation of "/ proc/ kallsyms", the table kallsyms_names [] is still stored in ascending order corresponding to the address one-to-one.

Add the array kallsyms_seqs_of_names [], which is indexed by the sequence number of the sorted name, and the corresponding content is the sequence number of the sorted address.

For example, suppose that the index of NameX in the array kallsyms_seqs_of_names [] is'I', and the content of NameX is'k', then the corresponding address of NameX is kallsyms_addresses [k]. The offset in kallsyms_names [] is get_symbol_offset (k).

Note that memory usage will increase by (4 * kallsyms_num_syms) bytes, and the next two patches will reduce (1 * kallsyms_num_syms) bytes and properly handle the case of CONFIG_LTO_CLANG=y.

Performance test results (on x86 platform):

Before:

Min=234, max=10364402, avg=5206926

Min=267, max=11168517, avg=5207587

After that:

Min=1016, max=90894, avg=7272

Min=1014, max=93470, avg=7293

The average query performance of kallsyms_lookup_name () is improved by 715 times. This is a major improvement for kallsyms_lookup_name and a Christmas present for Linux 6.2.

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