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, 05 May 2014 09:59:11 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	mingo@...nel.org, linux-tip-commits@...r.kernel.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.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

On Mon, 2014-05-05 at 18:31 +0200, Peter Zijlstra wrote:
> On Mon, May 05, 2014 at 09:03:28AM -0700, Tim Chen 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.
> 
> Wouldn't a state diagram be clearer than this gobs of text?

The state is represented by the count field with an explanation
of what each state actually means.  I started off with a
pretty abbreviated version. But to account for the readers and writers
that are in transient trying to acquire the lock, the comments
get more verbose, unfortunately.

Tim

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