linux-kernel - Re: [tip:locking/core] rwsem: Add comments to explain the meaning of the rwsem's count field

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Date:	Mon, 5 May 2014 20:27:50 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	linux-tip-commits@...r.kernel.org, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	peter@...leysoftware.com, jason.low2@...com, riel@...hat.com,
	alex.shi@...aro.org, paulmck@...ux.vnet.ibm.com,
	akpm@...ux-foundation.org, tglx@...utronix.de, walken@...gle.com,
	davidlohr@...com, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [tip:locking/core] rwsem: Add comments to explain the meaning of
 the rwsem's count field


* Tim Chen <tim.c.chen@...ux.intel.com> wrote:

> On Mon, 2014-05-05 at 19:26 +0200, Ingo Molnar wrote:
> > * Tim Chen <tim.c.chen@...ux.intel.com> wrote:
> > 
> > > On Mon, 2014-05-05 at 01:46 -0700, tip-bot for Tim Chen wrote:
> > > > Commit-ID:  3cf2f34e1a3d4d5ff209d087925cf950e52f4805
> > > > Gitweb:     http://git.kernel.org/tip/3cf2f34e1a3d4d5ff209d087925cf950e52f4805
> > > > Author:     Tim Chen <tim.c.chen@...ux.intel.com>
> > > > AuthorDate: Fri, 2 May 2014 12:53:57 -0700
> > > > Committer:  Ingo Molnar <mingo@...nel.org>
> > > > CommitDate: Sun, 4 May 2014 20:34:26 +0200
> > > > 
> > > 
> > > Ingo,
> > > 
> > > Can you pick up this version of the patch instead.  I've updated the 
> > > comments to reflect all cases for which the rwsem's count is less 
> > > than WAITING_BIAS, as Peter has pointed out.
> > 
> > Please send a delta patch against the one I applied - and also the 
> > state diagram suggestion with Peter, once it's clear what form it 
> > should take. I've yet to see a state diagram that was inferior to 
> > equivalent textual description - is this case an exception to that?
> > 
> 
> Ingo,
> 
> The delta patch is included below.  Thinking a bit more,
> the state diagram approach is not necessarily less verbose
> because the state is a tuple (count, wait queue state).
> After enumerating the states, we may wind up with very similar
> to what I have.

Could we at least try with one diagram and see how it goes?

Thanks,

	Ingo
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