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

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  [PATCH v2] livepatch: Reduce the time of finding module symbols Zhou Chengming <zhouchengming1@huawei.com> - 2017-03-28 15:20 +0200
    Re: [PATCH v2] livepatch: Reduce the time of finding module symbols Josh Poimboeuf <jpoimboe@redhat.com> - 2017-03-29 17:10 +0200
    Re: [PATCH v2] livepatch: Reduce the time of finding module symbols Jessica Yu <jeyu@redhat.com> - 2017-03-29 21:50 +0200
    Re: [PATCH v2] livepatch: Reduce the time of finding module  symbols Miroslav Benes <mbenes@suse.cz> - 2017-03-30 10:10 +0200
    Re: [PATCH v2] livepatch: Reduce the time of finding module  symbols Jiri Kosina <jikos@kernel.org> - 2017-03-30 10:50 +0200

#1610843 — [PATCH v2] livepatch: Reduce the time of finding module symbols

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@huawei.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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#1612028

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@huawei.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@redhat.com>

-- 
Josh

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#1612278

+++ 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@huawei.com>

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

Acked-by: Jessica Yu <jeyu@redhat.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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>the body of a message to majordomo@vger.kernel.org
>More majordomo info at  http://vger.kernel.org/majordomo-info.html

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#1612693 — Re: [PATCH v2] livepatch: Reduce the time of finding module symbols

On Tue, 28 Mar 2017, 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@huawei.com>

We are the only user of kallsyms_on_each_symbol() interface right now, so 
it is not that bad to optimize here. Temporarily :)

Acked-by: Miroslav Benes <mbenes@suse.cz>

Miroslav

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#1612738 — Re: [PATCH v2] livepatch: Reduce the time of finding module symbols

On Tue, 28 Mar 2017, Zhou Chengming wrote:

> It's reported that the time of insmoding a klp.ko for one of our
> out-tree modules is too long.

Applied to for-4.12/upstream. Thanks,

-- 
Jiri Kosina
SUSE Labs

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