Message-ID: <1438025945.25997.46.camel@stgolabs.net>
Subject: Re: [PATCH v3 2/7] locking/pvqspinlock: Add pending bit support
From: Davidlohr Bueso <dave@stgolabs.net>
To: Waiman Long <waiman.long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        x86@kernel.org, linux-kernel@vger.kernel.org,
        Scott J Norton <scott.norton@hp.com>,
        Douglas Hatch <doug.hatch@hp.com>
Date: Mon, 27 Jul 2015 12:39:05 -0700
In-Reply-To: <55B66ACB.6010702@hp.com>
References: <1437595962-21472-1-git-send-email-Waiman.Long@hp.com>
	 <1437595962-21472-3-git-send-email-Waiman.Long@hp.com>
	 <1437958584.25997.27.camel@stgolabs.net> <55B66ACB.6010702@hp.com>
Content-Type: text/plain; charset="UTF-8"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 790
Lines: 30

On Mon, 2015-07-27 at 13:30 -0400, Waiman Long wrote:
> The pending bit acts as a 1-slot waiting queue. So if the vCPU needs to 
> fall back to regular queuing, it needs to clear the bit.

Right, that's what I thought. So you would also need to call
clear_pending() as soon as the trylock/pending loop hits zero. Or am I
missing something?

/*
 * trylock || pending
 */
for (;;) {
	...
	if (loop--<= 0) {
		clear_pending(lock);
		goto queue;
	}
}

Also, no need to check for negative loop, zero should be enough to
breakout.

Thanks,
Davidlohr

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/