linux-kernel - Re: [PATCH 2/2] timer: really raise softirq if there is irq

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Message-ID: <20140131200535.GR5002@laptop.programming.kicks-ass.net>
Date:	Fri, 31 Jan 2014 21:05:35 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>, paulmck@...ux.vnet.ibm.com,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	tglx@...utronix.de, Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 2/2] timer: really raise softirq if there is irq_work to
 do

On Fri, Jan 31, 2014 at 08:48:45PM +0100, Sebastian Andrzej Siewior wrote:
> 
> How "bad" is it? Is this something generic or just not getting
> perf events fast enough out? Most users don't seem to require small
> latencies.

I have vague memories of there being an actual perf problem if there's a
hole between the NMI/IRQ triggering the irq_work and the interrupt
running the work.

I should have some notes on it somewhere and an todo entry to plug the
hole.

But note that the MCE code also uses irq_work, they really _need_ to be
fast because the system might be crumbling under their feet.
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