linux-kernel - Re: [PATCH v2 0/8] kallsyms: Optimizes the performance of lookup symbols

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Date:   Fri, 16 Sep 2022 11:17:17 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        <live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Luis Chamberlain" <mcgrof@...nel.org>,
        <linux-modules@...r.kernel.org>
Subject: Re: [PATCH v2 0/8] kallsyms: Optimizes the performance of lookup
 symbols



On 2022/9/16 9:27, Leizhen (ThunderTown) wrote:
> Hi, everybody:
>   Can anyone review it? Maybe I should split this patch series
> into two parts: kallsyms and livepatch.
>   In fact, the performance can be improved even if the compression policy
> of the symbol type is not changed, that is, the scripts/callsyms.c file is
> not modified, but we perform the len-based filtering first. That way, it'll
> be easier for everyone to review. OK, I'm ready for v3.

Sorry, I didn't sleep well yesterday. The length is the length of the
compressed string. Therefore, the solution is not feasible.

> 
> 
> On 2022/9/9 21:00, Zhen Lei wrote:
>> v1 --> v2:
>> Add self-test facility
>>
>> v1:
>> Currently, to search for a symbol, we need to expand the symbols in
>> 'kallsyms_names' one by one, and then use the expanded string for
>> comparison. This is very slow.
>>
>> In fact, we can first compress the name being looked up and then use
>> it for comparison when traversing 'kallsyms_names'.
>>
>> This patch series optimizes the performance of function kallsyms_lookup_name(),
>> and function klp_find_object_symbol() in the livepatch module. Based on the
>> test results, the performance overhead is reduced to 5%. That is, the
>> performance of these functions is improved by 20 times.
>>
>> To avoid increasing the kernel size in non-debug mode, the optimization is only
>> for the case CONFIG_KALLSYMS_ALL=y.
>>
>> Zhen Lei (8):
>>   scripts/kallsyms: don't compress symbol type when
>>     CONFIG_KALLSYMS_ALL=y
>>   scripts/kallsyms: rename build_initial_tok_table()
>>   kallsyms: Adjust the types of some local variables
>>   kallsyms: Improve the performance of kallsyms_lookup_name()
>>   kallsyms: Add helper kallsyms_on_each_match_symbol()
>>   livepatch: Use kallsyms_on_each_match_symbol() to improve performance
>>   livepatch: Improve the search performance of
>>     module_kallsyms_on_each_symbol()
>>   kallsyms: Add self-test facility
>>
>>  include/linux/kallsyms.h   |   8 ++
>>  init/Kconfig               |  13 ++
>>  kernel/Makefile            |   1 +
>>  kernel/kallsyms.c          | 135 ++++++++++++++++++++-
>>  kernel/kallsyms_selftest.c | 243 +++++++++++++++++++++++++++++++++++++
>>  kernel/livepatch/core.c    |  25 +++-
>>  kernel/module/kallsyms.c   |  13 +-
>>  scripts/kallsyms.c         |  19 ++-
>>  8 files changed, 441 insertions(+), 16 deletions(-)
>>  create mode 100644 kernel/kallsyms_selftest.c
>>
> 

-- 
Regards,
  Zhen Lei