linux-kernel - Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for this_cpu

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Date:	Tue, 20 Sep 2011 11:17:54 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Christoph Lameter <cl@...two.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Valdis.Kletnieks@...edu,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for
 this_cpu_read/write()

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



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