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locking/lockdep: Check redundant dependency only when CONFIG_LOCKDEP_SMALL 

As Peter has put it all sound and complete for the cause, I simply quote:

"It (check_redundant) was added for cross-release (which has since been
reverted) which would generate a lot of redundant links (IIRC) but
having it makes the reports more convoluted -- basically, if we had an
A-B-C relation, then A-C will not be added to the graph because it is
already covered. This then means any report will include B, even though
a shorter cycle might have been possible."

This would increase the number of direct dependencies. For a simple workload
(make clean; reboot; make vmlinux -j8), the data looks like this:

 CONFIG_LOCKDEP_SMALL: direct dependencies:                  6926

!CONFIG_LOCKDEP_SMALL: direct dependencies:                  9052    (+30.7%)

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Yuyang Du <duyuyang@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: bvanassche@acm.org
Cc: frederic@kernel.org
Cc: ming.lei@redhat.com
Cc: will.deacon@arm.com
Link: https://lkml.kernel.org/r/20190506081939.74287-21-duyuyang@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Yuyang Du 2019-05-06 16:19:36 +08:00 committed by Ingo Molnar
parent 8c2c2b449a
commit 68e9dc29f8
1 changed files with 4 additions and 0 deletions
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4
kernel/locking/lockdep.c
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@ -1739,6 +1739,7 @@ check_noncircular(struct held_lock *src, struct held_lock *target,
return ret;
}
#ifdef CONFIG_LOCKDEP_SMALL
/*
* Check that the dependency graph starting at <src> can lead to
* <target> or not. If it can, <src> -> <target> dependency is already
@ -1768,6 +1769,7 @@ check_redundant(struct held_lock *src, struct held_lock *target)
return ret;
}
#endif
#ifdef CONFIG_TRACE_IRQFLAGS
@ -2428,12 +2430,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
}
}
#ifdef CONFIG_LOCKDEP_SMALL
/*
* Is the <prev> -> <next> link redundant?
*/
ret = check_redundant(prev, next);
if (ret != 1)
return ret;
#endif
if (!trace->nr_entries && !save_trace(trace))
return 0;