From: mingo@kernel.org (Ingo Molnar)
To: linux-arm-kernel@lists.infradead.org
Subject: Dramatic lockdep slowdown in 4.14
Date: Sat, 14 Oct 2017 09:26:59 +0200
Message-ID: <20171014072659.f2yr6mhm5ha3eou7@gmail.com> (raw)
In-Reply-To: <20171013090333.GA17356@localhost>
* 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
next prev parent reply index
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-13 9:03 Johan Hovold
2017-10-13 9:07 ` Peter Zijlstra
2017-10-13 9:35 ` Johan Hovold
2017-10-14 7:26 ` Ingo Molnar [this message]
2017-10-14 8:11 ` Johan Hovold
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