Re: MPSAFE CAM?

From: Bruce Evans (bde_at_zeta.org.au)
Date: 05/31/05

  • Next message: M. Warner Losh: "Re: MPSAFE CAM?" 
    Date: Tue, 31 May 2005 11:39:47 +1000 (EST)
To: Robert Watson <rwatson@FreeBSD.org>

    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.

    Bruce
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  • Next message: M. Warner Losh: "Re: MPSAFE CAM?"