lkml.org 
[lkml]   [2017]   [Oct]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
SubjectRe: Dramatic lockdep slowdown in 4.14

* Johan Hovold <johan@kernel.org> wrote:

> Hi,
>
> I had noticed that the BeagleBone Black boot time appeared to have
> increased significantly with 4.14 and yesterday I finally had time to
> investigate it.
>
> Boot time (from "Linux version" to login prompt) had in fact doubled
> since 4.13 where it took 17 seconds (with my current config) compared to
> the 35 seconds I now see with 4.14-rc4.
>
> I quick bisect pointed to lockdep and specifically the following commit:
>
> 28a903f63ec0 ("locking/lockdep: Handle non(or multi)-acquisition
> of a crosslock")
>
> which I've verified is the commit which doubled the boot time (compared
> to 28a903f63ec0^) (added by lockdep crossrelease series [1]).
>
> I also verified that simply disabling CONFIG_PROVE_LOCKING on 4.14-rc4
> brought boot time down to about 14 seconds.
>
> Now since it's lockdep I guess this can't really be considered a
> regression if these changes did improve lockdep correctness, but still,
> this dramatic slow down essentially forces me to disable PROVE_LOCKING
> by default on this system.
>
> Is this lockdep slowdown expected and desirable?

It's not desirable at all.

Does the patch below fix the regression for you - or does the introduction and
handling of ->nr_acquire hurt as well?

Thanks,

Ingo

====================>
lib/Kconfig.debug | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index c6401d325b0e..f5b40c1668ea 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1138,8 +1138,8 @@ config PROVE_LOCKING
select DEBUG_MUTEXES
select DEBUG_RT_MUTEXES if RT_MUTEXES
select DEBUG_LOCK_ALLOC
- select LOCKDEP_CROSSRELEASE
- select LOCKDEP_COMPLETIONS
+# select LOCKDEP_CROSSRELEASE
+# select LOCKDEP_COMPLETIONS
select TRACE_IRQFLAGS
default n
help
\
 
 \ /
  Last update: 2017-10-14 09:27    [W:1.588 / U:1.616 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site