* [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact [not found] <CGME20181009153959eucas1p1ab3c10ba4868a4e97a1bff24d8f34c41@eucas1p1.samsung.com> @ 2018-10-09 15:39 ` Lukasz Luba 2018-10-09 15:53 ` Nikolay Borisov 2018-10-09 17:29 ` Waiman Long 0 siblings, 2 replies; 4+ messages in thread From: Lukasz Luba @ 2018-10-09 15:39 UTC (permalink / raw) To: linux-kernel; +Cc: l.luba, b.zolnierkie, longman, mingo This patch add some comment related to performance impact, which can be really big (x3 times slower context switch). Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com> --- lib/Kconfig.debug | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 4966c4f..9e67a2a3 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1088,6 +1088,9 @@ config PROVE_LOCKING the proof of observed correctness is also maintained for an arbitrary combination of these separate locking variants. + This feature enables LOCKDEP which can harm system performance + even x3 times. + For more details, see Documentation/locking/lockdep-design.txt. config LOCK_STAT @@ -1112,6 +1115,10 @@ config LOCK_STAT CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. (CONFIG_LOCKDEP defines "acquire" and "release" events.) + This feature enables LOCKDEP which can harm system performance + even x3 times. + For more details, see Documentation/locking/lockdep-design.txt. + config DEBUG_RT_MUTEXES bool "RT Mutex debugging, deadlock detection" depends on DEBUG_KERNEL && RT_MUTEXES @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC spin_lock_init()/mutex_init()/etc., or whether there is any lock held during task exit. + This feature enables LOCKDEP which can harm system performance + even x3 times. + For more details, see Documentation/locking/lockdep-design.txt. + config LOCKDEP bool depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT -- 2.7.4 ^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact 2018-10-09 15:39 ` [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact Lukasz Luba @ 2018-10-09 15:53 ` Nikolay Borisov 2018-10-09 17:29 ` Waiman Long 1 sibling, 0 replies; 4+ messages in thread From: Nikolay Borisov @ 2018-10-09 15:53 UTC (permalink / raw) To: Lukasz Luba, linux-kernel; +Cc: b.zolnierkie, longman, mingo On 9.10.2018 18:39, Lukasz Luba wrote: > This patch add some comment related to performance impact, > which can be really big (x3 times slower context switch). > > Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com> I don't think this brings any value. lockdep is a debugging aid aimed at developers. A developer should be aware that it has a performance impact and the classification x3 doesn't really bring anything. > --- > lib/Kconfig.debug | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 4966c4f..9e67a2a3 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1088,6 +1088,9 @@ config PROVE_LOCKING > the proof of observed correctness is also maintained for an > arbitrary combination of these separate locking variants. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + > For more details, see Documentation/locking/lockdep-design.txt. > > config LOCK_STAT > @@ -1112,6 +1115,10 @@ config LOCK_STAT > CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. > (CONFIG_LOCKDEP defines "acquire" and "release" events.) > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config DEBUG_RT_MUTEXES > bool "RT Mutex debugging, deadlock detection" > depends on DEBUG_KERNEL && RT_MUTEXES > @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC > spin_lock_init()/mutex_init()/etc., or whether there is any lock > held during task exit. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config LOCKDEP > bool > depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact 2018-10-09 15:39 ` [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact Lukasz Luba 2018-10-09 15:53 ` Nikolay Borisov @ 2018-10-09 17:29 ` Waiman Long 2018-10-10 8:42 ` Lukasz Luba 1 sibling, 1 reply; 4+ messages in thread From: Waiman Long @ 2018-10-09 17:29 UTC (permalink / raw) To: Lukasz Luba, linux-kernel; +Cc: b.zolnierkie, mingo On 10/09/2018 11:39 AM, Lukasz Luba wrote: > This patch add some comment related to performance impact, > which can be really big (x3 times slower context switch). > > Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com> > --- > lib/Kconfig.debug | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index 4966c4f..9e67a2a3 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1088,6 +1088,9 @@ config PROVE_LOCKING > the proof of observed correctness is also maintained for an > arbitrary combination of these separate locking variants. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + > For more details, see Documentation/locking/lockdep-design.txt. > > config LOCK_STAT > @@ -1112,6 +1115,10 @@ config LOCK_STAT > CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. > (CONFIG_LOCKDEP defines "acquire" and "release" events.) > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config DEBUG_RT_MUTEXES > bool "RT Mutex debugging, deadlock detection" > depends on DEBUG_KERNEL && RT_MUTEXES > @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC > spin_lock_init()/mutex_init()/etc., or whether there is any lock > held during task exit. > > + This feature enables LOCKDEP which can harm system performance > + even x3 times. > + For more details, see Documentation/locking/lockdep-design.txt. > + > config LOCKDEP > bool > depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT I don't mind seeing warning message about the performance impact of enabling lockdep. However, the actual slowdown depends on many factors including the type of systems, workloads and so on. I am a bit hesitant to quote an actual figure like x3 in the help text as it may not be correct in many cases. BTW, my recent lockdep patch (https://lkml.org/lkml/2018/10/2/1410) should be able to reduce the performance impact of enabling lockdep. Could you try to see if that help in your case? Cheers, Longman ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact 2018-10-09 17:29 ` Waiman Long @ 2018-10-10 8:42 ` Lukasz Luba 0 siblings, 0 replies; 4+ messages in thread From: Lukasz Luba @ 2018-10-10 8:42 UTC (permalink / raw) To: Waiman Long, linux-kernel; +Cc: b.zolnierkie, mingo Hi Longman, Thanks for the patches. I have applied them and run on ARM. In context switch test, there is ~2% improvement (but still ~15us instead of 5-6us). In dhrystone: test results are the same. There is also 2% improvement in boot time. You can add me on CC list if you have some patches related to this feature. I will give it a try on arm platforms. Regards, Lukasz On 10/09/2018 07:29 PM, Waiman Long wrote: > On 10/09/2018 11:39 AM, Lukasz Luba wrote: >> This patch add some comment related to performance impact, >> which can be really big (x3 times slower context switch). >> >> Signed-off-by: Lukasz Luba <l.luba@partner.samsung.com> >> --- >> lib/Kconfig.debug | 11 +++++++++++ >> 1 file changed, 11 insertions(+) >> >> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug >> index 4966c4f..9e67a2a3 100644 >> --- a/lib/Kconfig.debug >> +++ b/lib/Kconfig.debug >> @@ -1088,6 +1088,9 @@ config PROVE_LOCKING >> the proof of observed correctness is also maintained for an >> arbitrary combination of these separate locking variants. >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + >> For more details, see Documentation/locking/lockdep-design.txt. >> >> config LOCK_STAT >> @@ -1112,6 +1115,10 @@ config LOCK_STAT >> CONFIG_LOCK_STAT defines "contended" and "acquired" lock events. >> (CONFIG_LOCKDEP defines "acquire" and "release" events.) >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + For more details, see Documentation/locking/lockdep-design.txt. >> + >> config DEBUG_RT_MUTEXES >> bool "RT Mutex debugging, deadlock detection" >> depends on DEBUG_KERNEL && RT_MUTEXES >> @@ -1175,6 +1182,10 @@ config DEBUG_LOCK_ALLOC >> spin_lock_init()/mutex_init()/etc., or whether there is any lock >> held during task exit. >> >> + This feature enables LOCKDEP which can harm system performance >> + even x3 times. >> + For more details, see Documentation/locking/lockdep-design.txt. >> + >> config LOCKDEP >> bool >> depends on DEBUG_KERNEL && LOCK_DEBUGGING_SUPPORT > > I don't mind seeing warning message about the performance impact of > enabling lockdep. However, the actual slowdown depends on many factors > including the type of systems, workloads and so on. I am a bit hesitant > to quote an actual figure like x3 in the help text as it may not be > correct in many cases. > > BTW, my recent lockdep patch (https://lkml.org/lkml/2018/10/2/1410) > should be able to reduce the performance impact of enabling lockdep. > Could you try to see if that help in your case? > > Cheers, > Longman > > > > ^ permalink raw reply [flat|nested] 4+ messages in thread
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2018-10-09 15:39 ` [PATCH] lib/Kconfig.debug: add a comment to PROVE_LOCKING impact Lukasz Luba
2018-10-09 15:53 ` Nikolay Borisov
2018-10-09 17:29 ` Waiman Long
2018-10-10 8:42 ` Lukasz Luba
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