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

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Message-ID: <20170329194041.7kqbgwculigwiq3d@jeyu>
Date:   Wed, 29 Mar 2017 12:40:41 -0700
From:   Jessica Yu <jeyu@...hat.com>
To:     Zhou Chengming <zhouchengming1@...wei.com>
Cc:     live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        jpoimboe@...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

+++ 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@...wei.com>

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

Acked-by: Jessica Yu <jeyu@...hat.com>

>---
> 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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