linux-kernel - Re: [PATCH 0/7] kallsyms: Optimizes the performance of lookup symbols

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Date:   Thu, 8 Sep 2022 17:07:39 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     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>,
        linux-modules@...r.kernel.org
Subject: Re: [PATCH 0/7] kallsyms: Optimizes the performance of lookup symbols

On Thu, Sep 08, 2022 at 09:09:29PM +0800, Zhen Lei wrote:
> 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.

WIthout having time yet to reveiw the implementation details, it would
seem this is an area we may want to test for future improvements easily,
so a selftest better yet a kunit test may be nice for this. Can you
write one so we can easily gather a simple metric for "how long does
this take"?

  Luis