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Date: Wed, 8 Aug 2018 12:59:40 +0300
From: Kirill Tkhai <ktkhai@...tuozzo.com>
To: Stephen Rothwell <sfr@...b.auug.org.au>
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Subject: Re: [PATCH RFC 01/10] rcu: Make CONFIG_SRCU unconditionally enabled
On 08.08.2018 04:08, Stephen Rothwell wrote:
> Hi Kirill,
>
> On Tue, 07 Aug 2018 18:37:36 +0300 Kirill Tkhai <ktkhai@...tuozzo.com> wrote:
>>
>> This patch kills all CONFIG_SRCU defines and
>> the code under !CONFIG_SRCU.
>>
>> Signed-off-by: Kirill Tkhai <ktkhai@...tuozzo.com>
>
> So what sort of overheads (in terms of code size and performance) are
> we adding by having SRCU enabled where it used not to be?
SRCU is unconditionally enabled for x86, so I had to use another arch (sparc64)
to check the size difference. The config, I used to compile, is attached, SRCU
was enabled via:
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 2d58c26bff9a..6e9116e356d4 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -15,6 +15,7 @@ config SPARC
select ARCH_MIGHT_HAVE_PC_PARPORT if SPARC64 && PCI
select ARCH_MIGHT_HAVE_PC_SERIO
select OF
+ select SRCU
select OF_PROMTREE
select HAVE_IDE
select HAVE_OPROFILE
$ size image.srcu.disabled
text data bss dec hex filename
5117546 8030506 1968104 15116156 e6a77c image.srcu.disabled
$ size image.srcu.enabled
text data bss dec hex filename
5126175 8064346 1968104 15158625 e74d61 image.srcu.enabled
The difference is: 15158625-15116156 = 42469 ~41Kb
I have not ideas about performance overhead measurements. If you have ideas,
where they may occur, please say. At the first sight, there should not be
a problem, since SRCU is enabled in x86 by default.
View attachment ".config" of type "text/plain" (65783 bytes)
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