Date: Thu, 15 Dec 2005 15:38:18 -0500
From: Jeff Dike <jdike@addtoit.com>
To: "Luck, Tony" <tony.luck@intel.com>
Cc: dhowells@redhat.com, Andrew Morton <akpm@osdl.org>,
       Mark Lord <lkml@rtr.ca>, tglx@linutronix.de, alan@lxorguk.ukuu.org.uk,
       pj@sgi.com, mingo@elte.hu, hch@infradead.org, torvalds@osdl.org,
       arjan@infradead.org, matthew@wil.cx, linux-kernel@vger.kernel.org,
       linux-arch@vger.kernel.org
Subject: Re: [PATCH 1/19] MUTEX: Introduce simple mutex implementation
Message-ID: <20051215203818.GA11487@ccure.user-mode-linux.org>
References: <B8E391BBE9FE384DAA4C5C003888BE6F0535A549@scsmsx401.amr.corp.intel.com>
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On Thu, Dec 15, 2005 at 09:45:10AM -0800, Luck, Tony wrote:
> There was a USENIX paper a couple of decades ago that described how
> to do a fast s/w disable of interrupts on machines where really disabling
> interrupts was expensive.  The rough gist was that the spl[1-7]()
> functions would just set a flag in memory to hold the desired interrupt
> mask.  If an interrupt actually occurred when it was s/w blocked, the
> handler would set a pending flag, and just rfi with interrupts disabled.
> Then the splx() code checked to see whether there was a pending interrupt
> and dealt with it if there was.

... and this is currently implemented (but not yet merged to mainline) in
UML.

				Jeff
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