linux-kernel - Re: [PATCH v2] livepatch: Reduce the time of finding module symbols

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Message-ID: <20170329145907.a2y7uvysxj52jix2@treble>
Date:   Wed, 29 Mar 2017 09:59:07 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Zhou Chengming <zhouchengming1@...wei.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        jeyu@...hat.com, jikos@...nel.org, mbenes@...e.cz,
        pmladek@...e.com, huawei.libin@...wei.com
Subject: Re: [PATCH v2] livepatch: Reduce the time of finding module symbols

On Tue, Mar 28, 2017 at 09:10:35PM +0800, Zhou Chengming wrote:
> It's reported that the time of insmoding a klp.ko for one of our
> out-tree modules is too long.
> 
> ~ time sudo insmod klp.ko
> real	0m23.799s
> user	0m0.036s
> sys	0m21.256s
> 
> Then we found the reason: our out-tree module used a lot of static local
> variables, so klp.ko has a lot of relocation records which reference the
> module. Then for each such entry klp_find_object_symbol() is called to
> resolve it, but this function uses the interface kallsyms_on_each_symbol()
> even for finding module symbols, so will waste a lot of time on walking
> through vmlinux kallsyms table many times.
> 
> This patch changes it to use module_kallsyms_on_each_symbol() for modules
> symbols. After we apply this patch, the sys time reduced dramatically.
> 
> ~ time sudo insmod klp.ko
> real	0m1.007s
> user	0m0.032s
> sys	0m0.924s
> 
> Signed-off-by: Zhou Chengming <zhouchengming1@...wei.com>

It would be good to make kallsyms faster, but either way this still a
performance improvement for patching modules.

Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>

-- 
Josh