RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation

From	박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com) <byungchul.park@lge.com>
Newsgroups	linux.kernel
Subject	RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
Date	2017-09-01 14:10 +0200
Message-ID	<ukSVP-4fd-9@gated-at.bofh.it> (permalink)
References	(6 earlier) <uksRI-3bX-33@gated-at.bofh.it> <uktb4-3io-23@gated-at.bofh.it> <ukJzb-5GI-15@gated-at.bofh.it> <ukQKm-25K-17@gated-at.bofh.it> <ukRdn-2z9-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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> -----Original Message-----
> From: Byungchul Park [mailto:byungchul.park@lge.com]
> Sent: Friday, September 01, 2017 7:16 PM
> To: Peter Zijlstra
> Cc: mingo@kernel.org; tj@kernel.org; boqun.feng@gmail.com;
> david@fromorbit.com; johannes@sipsolutions.net; oleg@redhat.com; linux-
> kernel@vger.kernel.org; kernel-team@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?

Thread

Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-29 11:10 +0200
  [tip:locking/core] locking/lockdep: Untangle xhlock history  save/restore from task independence tip-bot for Peter Zijlstra <tipbot@zytor.com> - 2017-08-29 16:30 +0200
  Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-08-29 18:10 +0200
    Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-29 20:50 +0200
  Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 04:20 +0200
    Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 09:50 +0200
      Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:00 +0200
        RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:10 +0200
          Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:20 +0200
            RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:40 +0200
          Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-30 11:20 +0200
            RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation "Byungchul Park" <byungchul.park@lge.com> - 2017-08-30 11:30 +0200
              Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-30 13:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-08-30 15:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-31 09:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-08-31 10:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-01 04:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 11:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-01 12:20 +0200
                RE: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation 박병철/선임연구원/SW Platform(연)AOT팀(byungchul.park@lge.com)          <byungchul.park@lge.com> - 2017-09-01 14:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 14:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <max.byungchul.park@gmail.com> - 2017-09-01 16:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-01 18:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-04 03:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-04 04:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-04 13:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 02:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 09:10 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 09:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 11:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 11:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 12:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 13:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 15:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 02:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Boqun Feng <boqun.feng@gmail.com> - 2017-09-06 02:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 03:40 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-07 02:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-07 02:20 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-06 02:50 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-09-05 13:00 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 13:30 +0200
                Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Byungchul Park <byungchul.park@lge.com> - 2017-09-05 10:40 +0200
              Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Peter Zijlstra <peterz@infradead.org> - 2017-08-31 10:10 +0200

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