| Message ID | 20171014072659.f2yr6mhm5ha3eou7@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat, Oct 14, 2017 at 09:26:59AM +0200, Ingo Molnar wrote: > > * 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? > - select LOCKDEP_CROSSRELEASE > - select LOCKDEP_COMPLETIONS > +# select LOCKDEP_CROSSRELEASE > +# select LOCKDEP_COMPLETIONS Disabling these options this way gives me a about boot time of 17 seconds again, so yes, that fixes the problem. Thanks, Johan
====================> 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