linux-kernel - Re: [PATCH v2 5/6] locking/pvqspinlock: Opportunistically defer kicking to unlock time

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Message-ID: <20150716054911.GW19282@twins.programming.kicks-ass.net>
Date:	Thu, 16 Jul 2015 07:49:11 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Waiman Long <waiman.long@...com>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, Scott J Norton <scott.norton@...com>,
	Douglas Hatch <doug.hatch@...com>,
	Davidlohr Bueso <dave@...olabs.net>
Subject: Re: [PATCH v2 5/6] locking/pvqspinlock: Opportunistically defer
 kicking to unlock time

On Wed, Jul 15, 2015 at 10:18:35PM -0400, Waiman Long wrote:
> On 07/15/2015 06:03 AM, Peter Zijlstra wrote:

> >*groan*, so you complained the previous version of this patch was too
> >complex, but let me say I vastly preferred it to this one :/
> 
> I said it was complex as maintaining a tri-state variable needed more
> thought than 2 bi-state variables. I can revert it back to the tri-state
> variable as doing an unconditional kick in unlock simplifies the code at
> pv_wait_head().

Well, your state space isn't shrunk, you just use more variables and I'm
not entirely sure that actually matters.

What also doesn't help is that mixing with the kicking code.
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