MIME-Version: 1.0
In-Reply-To: <53050501.3070101@hp.com>
References: <1392669684-4807-1-git-send-email-Waiman.Long@hp.com>
	<53029167.4060109@zytor.com>
	<20140218073111.GW27965@twins.programming.kicks-ass.net>
	<5303B4C4.2040907@hp.com>
	<20140218212827.GR14089@laptop.programming.kicks-ass.net>
	<5303FDEC.9060001@hp.com>
	<20140219085107.GG27965@twins.programming.kicks-ass.net>
	<53050501.3070101@hp.com>
Date: Wed, 19 Feb 2014 12:17:15 -0800
Message-ID: <CA+55aFwyVgLJq2OgKZBK7g+T5-_M4o+dnEAr+qtYxA5t_=HSvA@mail.gmail.com>
Subject: Re: [PATCH v4 0/3] qspinlock: Introducing a 4-byte queue spinlock
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Peter Zijlstra <peterz@infradead.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michel Lespinasse <walken@google.com>,
        Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
        George Spelvin <linux@horizon.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Daniel J Blueman <daniel@numascale.com>,
        Alexander Fyodorov <halcy@yandex.ru>,
        Aswin Chandramouleeswaran <aswin@hp.com>,
        Scott J Norton <scott.norton@hp.com>,
        Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org

On Wed, Feb 19, 2014 at 11:24 AM, Waiman Long <waiman.long@hp.com> wrote:
>
> We do have a CONFIG_PARAVIRT macro that turns on or off PV support. The
> queue spinlock can be easily changed into an unfair lock which allows lock
> stealing. We could have a config option to make it unfair in the PARAVIRT
> environment, but I don't think Linus like the idea of an unfair lock.

I could care less for the paravirt case. As long as the native case
ends up being sane (even when CONFIG_PARAVIRT is set at compile time),
I'm fine.

When actually running in a paravirtualized environment, locks are
always going to have problems.

                  Linus
--
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/