> -----Original Message----- > From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx] > Sent: Wednesday, August 30, 2017 5:48 PM > To: Sergey Senozhatsky > Cc: Byungchul Park; Bart Van Assche; linux-kernel@xxxxxxxxxxxxxxx; linux- > block@xxxxxxxxxxxxxxx; martin.petersen@xxxxxxxxxx; axboe@xxxxxxxxx; linux- > scsi@xxxxxxxxxxxxxxx; sfr@xxxxxxxxxxxxxxxx; linux-next@xxxxxxxxxxxxxxx; > kernel-team@xxxxxxx > Subject: Re: possible circular locking dependency detected [was: linux- > next: Tree for Aug 22] > > On Wed, Aug 30, 2017 at 10:42:07AM +0200, Peter Zijlstra wrote: > > > > So the overhead looks to be spread out over all sorts, which makes it > > harder to find and fix. > > > > stack unwinding is done lots and is fairly expensive, I've not yet > > checked if crossrelease does too much of that. > > Aah, we do an unconditional stack unwind for every __lock_acquire() now. > It keeps a trace in the xhlocks[]. Yeah.. I also think this is most significant.. > > Does the below cure most of that overhead? > > diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index 44c8d0d17170..7b872036b72e 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -4872,7 +4872,7 @@ static void add_xhlock(struct held_lock *hlock) > xhlock->trace.max_entries = MAX_XHLOCK_TRACE_ENTRIES; > xhlock->trace.entries = xhlock->trace_entries; > xhlock->trace.skip = 3; > - save_stack_trace(&xhlock->trace); > + /* save_stack_trace(&xhlock->trace); */ > } > > static inline int same_context_xhlock(struct hist_lock *xhlock)
