Messages in this thread Patch in this message | | | Date | Wed, 25 Oct 2017 04:11:48 -0700 | From | tip-bot for Byungchul Park <> | Subject | [tip:locking/core] locking/lockdep: Add a boot parameter allowing unwind in cross-release and disable it by default |
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Commit-ID: d141babe4244945f1d001118578e0eb3ce12729d Gitweb: https://git.kernel.org/tip/d141babe4244945f1d001118578e0eb3ce12729d Author: Byungchul Park <byungchul.park@lge.com> AuthorDate: Wed, 25 Oct 2017 17:56:00 +0900 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 25 Oct 2017 12:19:01 +0200
locking/lockdep: Add a boot parameter allowing unwind in cross-release and disable it by default
Johan Hovold reported a heavy performance regression caused by lockdep cross-release:
> 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]).
Currently cross-release performs unwind on every acquisition, but that is very expensive.
This patch makes unwind optional and disables it by default and only records acquire_ip.
Full stack traces are sometimes required for full analysis, in which case a boot paramter, crossrelease_fullstack, can be specified.
On my qemu Ubuntu machine (x86_64, 4 cores, 512M), the regression was fixed. We measure boot times with 'perf stat --null --repeat 10 $QEMU', where $QEMU launches a kernel with init=/bin/true:
1. No lockdep enabled:
Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):
2.756558155 seconds time elapsed ( +- 0.09% )
2. Lockdep enabled:
Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):
2.968710420 seconds time elapsed ( +- 0.12% )
3. Lockdep enabled + cross-release enabled:
Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):
3.153839636 seconds time elapsed ( +- 0.31% )
4. Lockdep enabled + cross-release enabled + this patch applied:
Performance counter stats for 'qemu_booting_time.sh bzImage' (10 runs):
2.963669551 seconds time elapsed ( +- 0.11% )
I.e. lockdep cross-release performance is now indistinguishable from vanilla lockdep.
Bisected-by: Johan Hovold <johan@kernel.org> Analyzed-by: Thomas Gleixner <tglx@linutronix.de> Suggested-by: Thomas Gleixner <tglx@linutronix.de> Reported-by: Johan Hovold <johan@kernel.org> Signed-off-by: Byungchul Park <byungchul.park@lge.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: amir73il@gmail.com Cc: axboe@kernel.dk Cc: darrick.wong@oracle.com Cc: david@fromorbit.com Cc: hch@infradead.org Cc: idryomov@gmail.com Cc: johannes.berg@intel.com Cc: kernel-team@lge.com Cc: linux-block@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-mm@kvack.org Cc: linux-xfs@vger.kernel.org Cc: oleg@redhat.com Cc: tj@kernel.org Link: http://lkml.kernel.org/r/1508921765-15396-5-git-send-email-byungchul.park@lge.com Signed-off-by: Ingo Molnar <mingo@kernel.org> --- Documentation/admin-guide/kernel-parameters.txt | 3 +++ kernel/locking/lockdep.c | 19 +++++++++++++++++-- 2 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 0549662..f20ed5e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -709,6 +709,9 @@ It will be ignored when crashkernel=X,high is not used or memory reserved is below 4G. + crossrelease_fullstack + [KNL] Allow to record full stack trace in cross-release + cryptomgr.notests [KNL] Disable crypto self-tests diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index e36e652..160b5d6 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -76,6 +76,15 @@ module_param(lock_stat, int, 0644); #define lock_stat 0 #endif +static int crossrelease_fullstack; +static int __init allow_crossrelease_fullstack(char *str) +{ + crossrelease_fullstack = 1; + return 0; +} + +early_param("crossrelease_fullstack", allow_crossrelease_fullstack); + /* * lockdep_lock: protects the lockdep graph, the hashes and the * class/list/hash allocators. @@ -4863,8 +4872,14 @@ static void add_xhlock(struct held_lock *hlock) xhlock->trace.nr_entries = 0; xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES; xhlock->trace.entries = xhlock->trace_entries; - xhlock->trace.skip = 3; - save_stack_trace(&xhlock->trace); + + if (crossrelease_fullstack) { + xhlock->trace.skip = 3; + save_stack_trace(&xhlock->trace); + } else { + xhlock->trace.nr_entries = 1; + xhlock->trace.entries[0] = hlock->acquire_ip; + } } static inline int same_context_xhlock(struct hist_lock *xhlock)
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