Date: Tue, 31 May 2005 11:39:47 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Robert Watson <rwatson@FreeBSD.org> Cc: daniel_k_eriksson@telia.com, freebsd-arch@FreeBSD.org Subject: Re: MPSAFE CAM? Message-ID: <20050531113008.R91505@delplex.bde.org> In-Reply-To: <20050530182650.R90885@fledge.watson.org> References: <!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA0VcX9IoJqUaXPS8MjT1PdsKAAAAQAAAAvHxW/c0DGk%2B3ez1DZggmFgEAAAAA@telia.com> <4298E316.9020303@samsco.org> <20050529121224.L52379@fledge.watson.org> <20050530.102803.74664036.imp@bsdimp.com> <20050530182650.R90885@fledge.watson.org>
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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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