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From: zhouchengming <zhouchengming1@huawei.com>
To: Miroslav Benes <mbenes@suse.cz>
Cc: <live-patching@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<jpoimboe@redhat.com>, <jeyu@redhat.com>, <jikos@kernel.org>,
	<pmladek@suse.com>, <huawei.libin@huawei.com>
Subject: Re: [PATCH] reduce the time of finding symbols for module
Date: Tue, 28 Mar 2017 18:58:54 +0800	[thread overview]
Message-ID: <58DA41EE.90607@huawei.com> (raw)
In-Reply-To: <alpine.LSU.2.20.1703281055550.30237@pobox.suse.cz>

On 2017/3/28 17:00, Miroslav Benes wrote:
>
> Hi,
>
> 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
>
> Is this stable through several (>=10) runs? 23 seconds are really
> suspicious. Yes, there is a linear search through all the kallsyms in
> kallsyms_on_each_symbol(), but there are something like 70k symbols on my
> machine (that is, way less than 1M). 23 seconds are somewhat unexpected.
>

Yes, it's stable through several runs.

I think the big reason is that our out-tree module used a lot of static local
variables. We can see '.rela.kpatch.dynrelas' contains many entries, so it will
waste a lot of time if we use kallsyms_on_each_symbol() to find these symbols of module.

Relocation section '.rela.kpatch.funcs' at offset 0x382e0 contains 3 entries:
   Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 0
000000000020  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 8
000000000028  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0

Relocation section '.rela.kpatch.dynrelas' at offset 0x38328 contains 2562 entries:
   Offset          Info           Type           Sym. Value    Sym. Name + Addend
000000000000  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 14
000000000018  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 13
000000000020  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0
000000000040  003300000101 R_AARCH64_ABS64   0000000000000000 value_show + 20
000000000058  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 13
000000000060  000b00000101 R_AARCH64_ABS64   0000000000000000 .kpatch.strings + 0

> If it is a problem, can we fix kallsyms_on_each_symbol() and replace the
> linear search with something better? All users would benefit...
>

Yes, it's better if we can improve the linear search, but I can't think of that...

Thanks.

> Thanks,
> Miroslav
>
> .
>

  reply	other threads:[~2017-03-28 11:00 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-28  2:02 [PATCH] reduce the time of finding symbols for module Zhou Chengming
2017-03-28  9:00 ` Miroslav Benes
2017-03-28 10:58   ` zhouchengming [this message]
2017-03-28 11:16     ` Miroslav Benes
2017-03-28 12:50       ` zhouchengming
2017-03-29  0:03       ` Jessica Yu
2017-03-29  1:50         ` Li Bin
2017-03-29 19:09           ` Jessica Yu
2017-10-13 12:54           ` Ruslan Bilovol
2017-10-13 13:18             ` Torsten Duwe
2017-10-17 12:44               ` Ruslan Bilovol
2017-10-17 13:06                 ` Torsten Duwe

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