MPSAFE CAM?

M. Warner Losh imp at bsdimp.com
Mon May 30 19:30:28 PDT 2005


In message: <20050531113008.R91505 at delplex.bde.org>
            Bruce Evans <bde at 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 at fledge.watson.org>
: >>            Robert Watson <rwatson at 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


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