linux-kernel - Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with hardirq preemption

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Message-Id: <1222251467.8277.73.camel@pasglop>
Date:	Wed, 24 Sep 2008 20:17:47 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Milton Miller <miltonm@....com>
Cc:	Sebastien Dugue <sebastien.dugue@...l.net>,
	Jan-Bernd Themann <ossthema@...ibm.com>,
	Christoph Raisch <RAISCH@...ibm.com>,
	Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...abs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH HACK] powerpc: quick hack to get a functional eHEA with
	hardirq preemption

On Wed, 2008-09-24 at 04:58 -0500, Milton Miller wrote:
> The per-interrupt mask and unmask calls have to go through RTAS, a
> single-threaded global context, which in addition to increasing
> path length will really limit scalability.  The interrupt controller
> poll and reject facilities are accessed through hypervisor calls
> which are comparable to a fast syscall, and parallel to all cpus.

Note also that the XICS code thus assumes, iirc, as does the cell IIC
code, that eoi is called on the -same- cpu that fetched the interrupt
initially. That assumption can be broken with IRQ threads no ?

Ben.


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