linux-kernel - Re: [RFC][PATCH 0/7] locking: qspinlock

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Date:	Tue, 11 Mar 2014 12:04:47 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Waiman Long <waiman.long@...com>, arnd@...db.de,
	linux-arch@...r.kernel.org, x86@...nel.org,
	linux-kernel@...r.kernel.org, rostedt@...dmis.org,
	akpm@...ux-foundation.org, walken@...gle.com, andi@...stfloor.org,
	riel@...hat.com, paulmck@...ux.vnet.ibm.com,
	torvalds@...ux-foundation.org, oleg@...hat.com
Subject: Re: [RFC][PATCH 0/7] locking: qspinlock


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Mar 11, 2014 at 11:45:03AM +0100, Ingo Molnar wrote:
> > 
> > * Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > Hi Waiman,
> > > 
> > > I promised you this series a number of days ago; sorry for the delay 
> > > I've been somewhat unwell :/
> > > 
> > > That said, these few patches start with a (hopefully) simple and 
> > > correct form of the queue spinlock, and then gradually build upon 
> > > it, explaining each optimization as we go.
> > > 
> > > Having these optimizations as separate patches helps twofold; 
> > > firstly it makes one aware of which exact optimizations were done, 
> > > and secondly it allows one to proove or disprove any one step; 
> > > seeing how they should be mostly identity transforms.
> > > 
> > > The resulting code is near to what you posted I think; however it 
> > > has one atomic op less in the pending wait-acquire case for NR_CPUS 
> > > != huge. It also doesn't do lock stealing; its still perfectly fair 
> > > afaict.
> > > 
> > > Have I missed any tricks from your code?
> > 
> > Waiman, you indicated in the other thread that these look good to 
> > you, right? If so then I can queue them up so that they form a 
> > base for further work.
> 
> Ah, no that was on the qrwlock; I think we managed to cross wires 
> somewhere.

Oops, too many q-locks ;-)

> I've got this entire pile waiting for something:
> 
>   lkml.kernel.org/r/20140210195820.834693028@...radead.org
> 
> That's 5 mutex patches and the 2 qrwlock patches. Not sure what to 
> do with them. To merge or not, that is the question.

Can merge them in tip:core/locking if there's no objections.

Thanks,

	Ingo
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