linux-kernel - Re: [PATCH] tinification: Make SRCU optional by using CONFIG

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Message-ID: <548112D8.70009@cn.fujitsu.com>
Date:	Fri, 5 Dec 2014 10:05:12 +0800
From:	Lai Jiangshan <laijs@...fujitsu.com>
To:	<paulmck@...ux.vnet.ibm.com>
CC:	Pranith Kumar <bobby.prani@...il.com>,
	<linux-kernel@...r.kernel.org>,
	Josh Triplett <josh@...htriplett.org>
Subject: Re: [PATCH] tinification: Make SRCU optional by using CONFIG_SRCU

On 12/05/2014 08:11 AM, Paul E. McKenney wrote:
> On Thu, Dec 04, 2014 at 06:50:24PM -0500, Pranith Kumar wrote:
>> SRCU is not necessary to be compiled by default in all cases. For tinification
>> efforts not compiling SRCU unless necessary is desirable.
>>
>> The current patch tries to make compiling SRCU optional by introducing a new
>> Kconfig option CONFIG_SRCU which is selected when any of the components making
>> use of SRCU are selected.
>>
>> If we do not select CONFIG_SRCU, srcu.o will not be compiled at all.
>>
>>    text    data     bss     dec     hex filename
>>    2007       0       0    2007     7d7 kernel/rcu/srcu.o
>>
>> Size of arch/powerpc/boot/zImage changes from
>>
>>    text    data     bss     dec     hex filename
>>  831552   64180   23944  919676   e087c arch/powerpc/boot/zImage : before
>>  829504   64180   23952  917636   e0084 arch/powerpc/boot/zImage : after
>>
>> so the savings are about ~2000 bytes.
>>
>> Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>> CC: Paul McKenney <paulmck@...ux.vnet.ibm.com>
>> CC: Josh Triplett <josh@...htriplett.org>
> 
> I have queued this for testing.
> 
> Josh, does this look reasonable to you?
> 
> Lai, any issues?
> 
> 							Thanx, Paul
> 
>> ---
>>  arch/arm/kvm/Kconfig     |  1 +
>>  arch/arm64/kvm/Kconfig   |  1 +
>>  arch/ia64/kvm/Kconfig    |  1 +
>>  arch/mips/kvm/Kconfig    |  1 +
>>  arch/powerpc/kvm/Kconfig |  1 +
>>  arch/s390/kvm/Kconfig    |  1 +
>>  arch/tile/kvm/Kconfig    |  1 +
>>  arch/x86/Kconfig         |  1 +
>>  arch/x86/kvm/Kconfig     |  1 +
>>  drivers/clk/Kconfig      |  1 +
>>  drivers/cpufreq/Kconfig  |  1 +
>>  drivers/devfreq/Kconfig  |  1 +
>>  drivers/md/Kconfig       |  1 +
>>  drivers/net/Kconfig      |  1 +
>>  fs/btrfs/Kconfig         |  1 +
>>  fs/notify/Kconfig        |  1 +
>>  init/Kconfig             | 10 ++++++++++
>>  kernel/notifier.c        |  3 +++
>>  kernel/rcu/Makefile      |  3 ++-
>>  lib/Kconfig.debug        |  1 +
>>  mm/Kconfig               |  1 +
>>  security/tomoyo/Kconfig  |  1 +
>>  22 files changed, 34 insertions(+), 1 deletion(-)

Miss fs/quota/Kconfig?

./fs/quota/dquot.c:100: * Operation of reading pointer needs srcu_read_lock(&dquot_srcu), and
./fs/quota/dquot.c:1609:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1657:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1695:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1724:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1756:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1797:	index = srcu_read_lock(&dquot_srcu);
./fs/quota/dquot.c:1827: * protect them by srcu_read_lock().

And

./drivers/base/power/opp.c:90:	struct srcu_notifier_head head;
./drivers/base/power/opp.c:439:		srcu_init_notifier_head(&dev_opp->head);
./drivers/base/power/opp.c:484:	srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ADD, new_opp);
./drivers/base/power/opp.c:564:		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_ENABLE,
./drivers/base/power/opp.c:567:		srcu_notifier_call_chain(&dev_opp->head, OPP_EVENT_DISABLE,
./drivers/base/power/opp.c:625:struct srcu_notifier_head *dev_pm_opp_get_notifier(struct device *dev)

===

include/linux/srcu.h and ./include/linux/notifier.h should also use
"#ifdef CONFIG_SRCU .... "


>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index ded8a67..1c581a0 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -137,6 +137,7 @@ config X86
>>  	select HAVE_ACPI_APEI_NMI if ACPI
>>  	select ACPI_LEGACY_TABLES_LOOKUP if ACPI
>>  	select X86_FEATURE_NAMES if PROC_FS
>> +	select SRCU




Why you select SRCU when X86?

>>
>> +config SRCU
>> +	bool "Sleepable form of RCU"

Why it has a title? Somebody need to select it manually for third party kernel module?

>> +	def_bool n
>> +	help
>> +	  This option selects the sleepable version of RCU. This version
>> +	  permits arbitrary sleeping or blocking within RCU read-side critical
>> +	  sections.

You used "form" and "version" at the same time.


>>
>> +#ifdef CONFIG_SRCU
>>  /*
>>   *	SRCU notifier chain routines.    Registration and unregistration
>>   *	use a mutex, and call_chain is synchronized by SRCU (no locks).
>> @@ -528,6 +529,8 @@ void srcu_init_notifier_head(struct srcu_notifier_head *nh)
>>  }
>>  EXPORT_SYMBOL_GPL(srcu_init_notifier_head);
>>
>> +#endif /* CONFIG_SRCU */

Do we need a new CONFIG_SRCU_NOTIFIER ?
--
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