linux-kernel - Re: [PATCH] Documentation: Remove misleading examples of the barriers in wake

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Message-ID: <20151012130924.GH27351@fixme-laptop.cn.ibm.com>
Date:	Mon, 12 Oct 2015 21:09:24 +0800
From:	Boqun Feng <boqun.feng@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, Jonathan Corbet <corbet@....net>,
	Michal Hocko <mhocko@...nel.org>,
	David Howells <dhowells@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] Documentation: Remove misleading examples of the
 barriers in wake_*()

On Mon, Oct 12, 2015 at 01:54:38PM +0200, Peter Zijlstra wrote:
> On Mon, Oct 12, 2015 at 05:06:36PM +0800, Boqun Feng wrote:
> > Understood.
> > 
> > But, IMO, the position of this section is already misleading:
> > 
> > (*) Implicit kernel memory barriers.
> >      - Locking functions.
> >      - Interrupt disabling functions.
> >    ->- Sleep and wake-up functions.<-
> >      - Miscellaneous functions.
> > 
> > I read it as that sleep and wake-up functions provide some kernel memory
> > barriers which we can use *externally*(outside sleep/wakeup themselves).
> 
> I think it is useful to state that the primitives handle the ordering
> between the waker and wakee wrt the 'blocking' state.
> 

I agree that's useful, however, the 'blocking' state is something
internal for sleep and wakeup, right? Not sure whether the users of
wake_up() and wait_event() will care much about this or they need to
understand that detailedly to use wake_up() and wait_event() correctly.

I treat this part of memory-barriers.txt as an API document to describe
the implicit barriers in some primitives, which can be used *externally*
by someone, but anyway, that's just my own opinion ;-)

> But I've not put much thought into wording. I wanted to finish process
> order 'comment' patch first.

Of course. Actually your 'comment' patch is the reason why I think this
section may be removed.

Regards,
Boqun

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