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

[Jessica Yu]

+++ Zhou Chengming [28/03/17 21:10 +0800]:
> 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@xxxxxxxxxx>

Limiting the search space for symbol lookups is a valid improvement, so:

Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

> ---
> kernel/livepatch/core.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index af46438..b4b8bb0 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -182,7 +182,10 @@ static int klp_find_object_symbol(const char *objname, const char *name,
> 	};
>
> 	mutex_lock(&module_mutex);
> -	kallsyms_on_each_symbol(klp_find_callback, &args);
> +	if (objname)
> +		module_kallsyms_on_each_symbol(klp_find_callback, &args);
> +	else
> +		kallsyms_on_each_symbol(klp_find_callback, &args);
> 	mutex_unlock(&module_mutex);
>
> 	/*
> --
> 1.8.3.1
>
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