Re: [PATCH] Documentation: Remove misleading examples of the barriers in wake_*()

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From	Boqun Feng <boqun.feng@gmail.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] Documentation: Remove misleading examples of the barriers in wake_*()
Date	Sun, 11 Oct 2015 17:30:01 +0200
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On Tue, Oct 06, 2015 at 06:06:50PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 24, 2015 at 09:21:22PM +0800, Boqun Feng wrote:
> > > Included in it are some of the details on this subject, because a wakeup
> > > has two prior states that are of importance, the tasks own prior state
> > > and the wakeup state, both should be considered in the 'program order'
> > > flow.
> > > 
> > 
> > Great and very helpful ;-)
> > 
> > > So maybe we can reduce the description in memory-barriers to this
> > > 'split' program order guarantee, where a woken task must observe both
> > > its own prior state and its wakee state.
> >                               ^^^^^
> > I think you mean "waker" here, right?
> 
> Yes.
> 
> > And the waker is not necessarily the same task who set the @cond to
> > true, right? 
> 
> It should be.
> 
> > If so, I feel like it's really hard to *use* this 'split'
> > program order guarantee in other places than sleep/wakeup itself. Could
> > you give an example? Thank you.
> 
> It was not meant to be used in any other scenario; the 'split' PO really
> is part of the whole sleep/wakeup. It does not apply to anything else.

Got it. So at this point, I think it's better to remove the entire
"Sleep and wake-up functions" section in memory-barriers.txt. Because
this order guarantee is not for other users except sleep/wakeup. Any
concern, Paul?

Regards,
Boqun

Thread

Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Peter Zijlstra <peterz@infradead.org> - 2015-10-06 18:10 +0200
  Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Boqun Feng <boqun.feng@gmail.com> - 2015-10-11 17:30 +0200
    Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-10-12 02:50 +0200
      Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Boqun Feng <boqun.feng@gmail.com> - 2015-10-12 11:10 +0200
        Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Peter Zijlstra <peterz@infradead.org> - 2015-10-12 14:00 +0200
          Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Boqun Feng <boqun.feng@gmail.com> - 2015-10-12 15:10 +0200
            Re: [PATCH] Documentation: Remove misleading examples of the  barriers in wake_*() Peter Zijlstra <peterz@infradead.org> - 2015-10-12 18:30 +0200

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