Commit d141babe authored by Byungchul Park's avatar Byungchul Park Committed by Ingo Molnar
Browse files

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:
 >
 >	28a903f6 ("locking/lockdep: Handle non(or multi)-acquisition
 >	               of a crosslock")
 >
 > which I've verified is the commit which doubled the boot time (compared
 > to 28a903f6

^) (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: default avatarJohan Hovold <johan@kernel.org>
Analyzed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Suggested-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reported-by: default avatarJohan Hovold <johan@kernel.org>
Signed-off-by: default avatarByungchul 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: default avatarIngo Molnar <mingo@kernel.org>
parent 24208435
......@@ -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
......
......@@ -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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