Date: Tue, 12 May 2015 11:33:49 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Gilad Ben Yossef <giladb@ezchip.com>, Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Tejun Heo <tj@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Christoph Lameter <cl@linux.com>,
        "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
        linux-doc@vger.kernel.org, linux-api@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] nohz: support PR_DATAPLANE_QUIESCE
Message-ID: <20150512093349.GH21418@twins.programming.kicks-ass.net>
References: <1431107927-13998-1-git-send-email-cmetcalf@ezchip.com>
 <1431107927-13998-5-git-send-email-cmetcalf@ezchip.com>
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On Fri, May 08, 2015 at 01:58:45PM -0400, Chris Metcalf wrote:
> This prctl() flag for PR_SET_DATAPLANE sets a mode that requires the
> kernel to quiesce any pending timer interrupts prior to returning
> to userspace.  When running with this mode set, sys calls (and page
> faults, etc.) can be inordinately slow.  However, user applications
> that want to guarantee that no unexpected interrupts will occur
> (even if they call into the kernel) can set this flag to guarantee
> that semantics.

Currently people hot-unplug and hot-plug the CPU to do this. Obviously
that's a wee bit horrible :-)

Not sure if a prctl like this is any better though. This is a CPU
properly not a process one.

ISTR people talking about 'quiesce' sysfs file, along side the hotplug
stuff, I can't quite remember.


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