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Subject: Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for
 this_cpu_read/write()
From: Steven Rostedt <rostedt@goodmis.org>
To: Christoph Lameter <cl@gentwo.org>
Cc: Thomas Gleixner <tglx@linutronix.de>, Valdis.Kletnieks@vt.edu,
        linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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Date: Tue, 20 Sep 2011 11:17:54 -0400
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On Tue, 2011-09-20 at 09:58 -0500, Christoph Lameter wrote:
> On Tue, 20 Sep 2011, Thomas Gleixner wrote:
> 
> > > What's the latency hit on those very few locations if we simply put our
> > > collective foot down and not support a preemptable version of this_cpu_*()?
> > > "Yes, you *could* preempt here, but for our collective sanity that's not
> > > supported"...
> >
> > Full ack.
> 
> Latency hit could be very significant in various critical kernel paths.
> Especially network subsystem, vm event counters etc.

Latency hit is better than incorrect behavior. I tell people working on
-rt all the time. A bug/kernel crash is much worse than a hit in
latency, as a bug/kernel crash causes a much bigger latency hit than
anything else.

-- Steve