MPSAFE CAM?
Bruce Evans
bde at zeta.org.au
Mon May 30 18:40:00 PDT 2005
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.
Bruce
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