> -----Original Message----- > From: Byungchul Park [mailto:byungchul.p...@lge.com] > Sent: Friday, September 01, 2017 7:16 PM > To: Peter Zijlstra > Cc: mi...@kernel.org; t...@kernel.org; boqun.f...@gmail.com; > da...@fromorbit.com; johan...@sipsolutions.net; o...@redhat.com; linux- > ker...@vger.kernel.org; kernel-t...@lge.com > Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation > > On Fri, Sep 01, 2017 at 11:47:47AM +0200, Peter Zijlstra wrote: > > On Fri, Sep 01, 2017 at 11:05:12AM +0900, Byungchul Park wrote: > > > On Thu, Aug 31, 2017 at 10:34:53AM +0200, Peter Zijlstra wrote: > > > > On Thu, Aug 31, 2017 at 05:15:01PM +0900, Byungchul Park wrote: > > > > > It's not important. Ok, check the following, instead: > > > > > > > > > > context X context Y > > > > > --------- --------- > > > > > wait_for_completion(C) > > > > > acquire(A) > > > > > release(A) > > > > > process_one_work() > > > > > acquire(B) > > > > > release(B) > > > > > work->fn() > > > > > complete(C) > > > > > > > > > > We don't need to lose C->A and C->B dependencies unnecessarily. > > > > > > > > I really can't be arsed about them. Its really only the first few > works > > > > that will retain that dependency anyway, even if you were to retain > > > > them. > > > > > > Wrong. > > > > > > Every 'work' doing complete() for different classes of completion > > > variable suffers from losing valuable dependencies, every time, not > > > first few ones. > > > > The moment you overrun the history array its gone. So yes, only the > > It would be gone _only_ at the time the history overrun, and then it > will be built again. So, you are wrong. > > Let me show you an example: (I hope you also show examples.) > > context X context Y > --------- --------- > wait_for_completion(D) > while (true) > acquire(A) > release(A) > process_one_work() > acquire(B) > release(B) > work->fn() > complete(C) > acquire(D) > release(D) > > When happening an overrun in a 'work', 'A' and 'B' will be gone _only_ > at the time, and then 'D', 'A' and 'B' will be queued into the xhlock > *again* from the next loop on, and they can be used to generate useful > dependencies again. > > You are being confused now. Acquisitions we are focusing now are not > _stacked_ like hlocks, but _accumulated_ continuously onto the ring > buffer e.i. xhlock array.
Agree?
