Subject: Re: possible circular locking dependency detected [was: linux-next: Tree for Aug 22]

From: Sergey Senozhatsky <[email-masked]>
Date: Wed, 30 Aug 2017 21:30:07 +0900

Hello Peter,

On (08/30/17 10:47), Peter Zijlstra wrote:
[..]
> 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[].
> 
> Does the below cure most of that overhead?

thanks.

mostly yes. the kernel is not so dramatically slower now. it's still
seems to be a bit slower, which is expected I suppose, but over all
it's much better

	real	1m35.209s
	user	4m12.467s
	sys	0m49.457s

// approx 10 seconds slower.

	-ss