From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Lars Segerlund <lars.segerlund@gmail.com>
Cc: linux-rt-users@vger.kernel.org
Subject: Re: rt & hotplug work....
Date: Fri, 20 Jul 2012 17:24:09 -0700 [thread overview]
Message-ID: <20120721002404.GA2435@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAF-VNaoh=t50=6A-OXitYPJxz67Es_jFQeqsXcdJThexb8uHSg@mail.gmail.com>
On Fri, Jul 20, 2012 at 10:07:38PM +0200, Lars Segerlund wrote:
> There was some cpu hotplug work recently, and I can't get my head
> around what happens with a dual cpu system if one core is shut down,
> specificly with spinlocks.
> Won't it just hang or spin a lot ? I was thinking the locking was
> different in the build for uni of multi processors, to eliminate the
> deadlock risk on a uni processor.
>
> I do realise this might not be rt specific, but I'll ask anyhow.
When a CPU-hotplug operation takes a CPU offline, that CPU must release
any true spinlocks before actually going away. Therefore, when the
surviving CPU attempts to acquire a spinlock, it is guaranteed to
acquire it immediately. (Some architectures go even farther and
optimize away spinlock acquisitions when the system transitions to
single-CPU operation.)
Thanx, Paul
prev parent reply other threads:[~2012-07-21 0:31 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-20 20:07 rt & hotplug work Lars Segerlund
2012-07-21 0:24 ` Paul E. McKenney [this message]
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