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Date: Mon, 30 May 2005 20:30:26 -0600 (MDT)
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To: bde@zeta.org.au
From: "M. Warner Losh" <imp@bsdimp.com>
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	<20050530182650.R90885@fledge.watson.org>
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Cc: rwatson@FreeBSD.org, daniel_k_eriksson@telia.com, freebsd-arch@FreeBSD.org
Subject: Re: MPSAFE CAM?
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In message: <20050531113008.R91505@delplex.bde.org>
            Bruce Evans <bde@zeta.org.au> writes:
: On Mon, 30 May 2005, Robert Watson wrote:
: 
: > On Mon, 30 May 2005, M. Warner Losh wrote:
: >
: >> In message: <20050529121224.L52379@fledge.watson.org>
: >>            Robert Watson <rwatson@FreeBSD.org> writes:
: >> : driver, we've gained many of the benefits of making MPSAFE.  Especially 
: >> if
: >> : we can knock Giant off a lot of the remaining non-CAM device drivers that
: >> : it's still stuck over.
: >> 
: >> usb, psm and atkbd are important ones for interactive performance...
: >
: > And the tty subsystem becomes an immediate dependency for several of these.
: 
: Interactive performance is irrelevant here.  You can can lose efficiency
: by competing for Giant a few hundred thousand times in the time that
: it takes an interactive user to notice.  The problem is that non-interactive
: performance is impaired by using Giant locking anywhere.  Using it for
: interactive devices is only a problem if the interaction often requires
: holding Giant for a long time.  It doesn't for most input devices
: including keyboards, but it might for slow bulk output devices like
: syscons consoles.

Also in the case of usb, it means that all devices sharing interrupts
with the usb bridges are effectively under giant...

Warner