linux-kernel - Re: [PATCH -tip -v5] irq_work: generic hard-irq context callbacks

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Date:	Fri, 17 Sep 2010 15:06:42 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Huang Ying <ying.huang@...el.com>
Cc:	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	paulus <paulus@...ba.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	dhowells <dhowells@...hat.com>,
	Russell King <rmk@....linux.org.uk>,
	Kyle McMartin <kyle@...artin.ca>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	davem <davem@...emloft.net>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH -tip -v5] irq_work: generic hard-irq context callbacks

On Fri, 2010-09-17 at 10:05 +0800, Huang Ying wrote:
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> 
> In order for other NMI context users that want to run things from
> hard-IRQ context, extract the perf_event callback mechanism.
> 
> Huang Ying: some fixes

I got complaints about a lacking changelog, how about something like the
below?

---

Provide a mechanism that allows running code in IRQ context. It is most
useful for NMI code that needs to interact with the rest of the system
-- like wakeup a task to drain buffers.

Perf currently has such a mechanism, so extract that and provide it as a
generic feature, independent of perf so that others may also benefit.

The IRQ context callback is generated through self-IPIs where possible,
or on architectures like powerpc which have soft-disabled IRQs, its ran
on the soft-enable path.

Architectures that don't have anything like this get to do with a
callback from the timer tick. These architectures can call
irq_run_work() at the tail of any IRQ handlers that might enqueue such
work (like the perf IRQ handler) to avoid undue latencies in processing
the work.

---
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