Re: [PATCH] tinification: Make SRCU optional by using CONFIG_SRCU

From: Lai Jiangshan
Date: Thu Dec 04 2014 - 21:01:27 EST


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@xxxxxxxxx>
>> CC: Paul McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>> CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
>
> 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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