From mboxrd@z Thu Jan  1 00:00:00 1970
From: jmk@plan9.bell-labs.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] Performance
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
Message-Id: <20010511135552.0DB18199D7@mail.cse.psu.edu>
Date: Fri, 11 May 2001 09:52:39 -0400
Topicbox-Message-UUID: 9f1bec40-eac9-11e9-9e20-41e7f4b1d025

On Fri May 11 04:42:36 EDT 2001, DAGwyn@null.net wrote:
> jmk@plan9.bell-labs.com wrote:
> > I think the correct kludge is to wait for the clock interrupt.
> 
> Also the most portable.

You learn something new every day. Charles Forsyth pointed out to me
that had I read the x86 description of the STI command as well as HLT
I would see there is no possibility of an interrupt occurring between
the sequence
	STI
	HLT
as the STI allows interrupts to be responded to after the completion
of the following instruction, and HLT is deemed to have completed when
it enters its halt state. Therefore, I think a possible way to close
the window on the x86 is

TEXT halt(SB), $0
	CLI
	CMPL	nrdy(SB), $0
	JEQ	_nothingready
	STI
	RET

_nothingready:
	STI
	HLT
	RET

Whether this is coded correctly or makes a difference is left as an
exercise for the student.

--jim