Date: Mon, 14 Sep 1998 17:22:29 -0700 From: David Greenman <dg@root.com> To: Terry Lambert <tlambert@primenet.com> Cc: joelh@gnu.org, tom@uniserve.com, gpalmer@FreeBSD.ORG, irc@cooltime.simplenet.com, freebsd-current@FreeBSD.ORG Subject: Re: Download of FreeBSD 3.0-SNAP Message-ID: <199809150022.RAA21739@implode.root.com> In-Reply-To: Your message of "Mon, 14 Sep 1998 18:11:38 -0000." <199809141811.LAA18415@usr05.primenet.com>
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>> I'm no disk expert, so please tell me: what is tagged command >> queueing? Is it the ability to have multiple outstanding requests, >> with the device reordering the requests for optimal efficiency, and >> relying on a cookie in the header to differentiate between requests? > >Yes. Think of it as "how much concurrency does my disk support?". >For a single-user, sincgle-program-at-a-time system, this is not >much of a bottleneck; for a server under load, it's the *primary* >bottleneck. > >Note that David points out that FreeBSD *does* do elevator sorting; >it's still not optimal, however, since physical and logical cylinder >boundaries are infrequently the same on modern hardware. I have >to look before I say any more (since I thought the code was removed >circa 2.2.1). David says it's called on all "dumb" drivers (wd, etc.); >I'm not sure the "Ultra" DMA EIDE drivers are still in this category. FreeBSD's disksort function sorts by block number, not by cylinder number. -DG David Greenman Co-founder/Principal Architect, The FreeBSD Project To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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