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

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Message-ID: <20100920042011.GA13542@drongo>
Date:	Mon, 20 Sep 2010 14:20:11 +1000
From:	Paul Mackerras <paulus@...ba.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Huang Ying <ying.huang@...el.com>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>,
	"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, Sep 17, 2010 at 03:06:42PM +0200, Peter Zijlstra wrote:

> 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.

Actually these days we do it by setting the decrementer (the built-in
timer facility) to generate an interrupt immediately (well, within one
timebase tick, i.e. a small number of nanoseconds).

Paul.
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