From: Boqun Feng <boqun.feng@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
Jonathan Corbet <corbet@lwn.net>,
Michal Hocko <mhocko@kernel.org>,
David Howells <dhowells@redhat.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] Documentation: Remove misleading examples of the barriers in wake_*()
Date: Thu, 24 Sep 2015 21:21:22 +0800 [thread overview]
Message-ID: <20150924132121.GA1814@fixme-laptop.cn.ibm.com> (raw)
In-Reply-To: <20150917130125.GL3816@twins.programming.kicks-ass.net>
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Hi Peter,
On Thu, Sep 17, 2015 at 03:01:26PM +0200, Peter Zijlstra wrote:
> On Thu, Sep 10, 2015 at 07:55:57PM +0200, Oleg Nesterov wrote:
> > On 09/10, Boqun Feng wrote:
> > >
> > > On Wed, Sep 09, 2015 at 12:28:22PM -0700, Paul E. McKenney wrote:
> > > > My feeling is
> > > > that we should avoid saying too much about the internals of wait_event()
> > > > and wake_up().
> >
> > I feel the same. I simply can't understand what we are trying to
> > document ;)
>
> So I've been sitting on this for a while and figured I'd finish it now.
>
> It are some notes on the scheduler locking and how it provides program
> order guarantees on SMP systems.
>
> 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?
And the waker is not necessarily the same task who set the @cond to
true, right? 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.
Regards,
Boqun
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next prev parent reply other threads:[~2015-09-24 13:21 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-08 1:14 [PATCH] Documentation: Remove misleading examples of the barriers in wake_*() Boqun Feng
2015-09-09 19:28 ` Paul E. McKenney
2015-09-10 2:16 ` Boqun Feng
2015-09-10 17:55 ` Oleg Nesterov
2015-09-11 16:59 ` Boqun Feng
2015-09-17 13:01 ` Peter Zijlstra
2015-09-17 17:01 ` Oleg Nesterov
2015-09-18 6:49 ` Peter Zijlstra
2015-09-21 17:46 ` Oleg Nesterov
2015-10-06 16:04 ` Peter Zijlstra
2015-10-06 16:24 ` Peter Zijlstra
2015-10-06 16:35 ` Will Deacon
2015-10-06 19:57 ` Peter Zijlstra
2015-10-07 11:10 ` Peter Zijlstra
2015-10-07 15:40 ` Paul E. McKenney
2015-09-24 13:21 ` Boqun Feng [this message]
2015-10-06 16:06 ` Peter Zijlstra
2015-10-11 15:26 ` Boqun Feng
2015-10-12 0:40 ` Paul E. McKenney
2015-10-12 9:06 ` Boqun Feng
2015-10-12 11:54 ` Peter Zijlstra
2015-10-12 13:09 ` Boqun Feng
2015-10-12 16:26 ` Peter Zijlstra
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