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Message-ID: <20150512093349.GH21418@twins.programming.kicks-ass.net>
Date: Tue, 12 May 2015 11:33:49 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Chris Metcalf <cmetcalf@...hip.com>
Cc: Gilad Ben Yossef <giladb@...hip.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Frederic Weisbecker <fweisbec@...il.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Christoph Lameter <cl@...ux.com>,
"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] nohz: support PR_DATAPLANE_QUIESCE
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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