Date: Tue, 15 Sep 1998 08:43:53 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: joelh@gnu.org Cc: Terry Lambert <tlambert@primenet.com>, tom@uniserve.com, gpalmer@FreeBSD.ORG, irc@cooltime.simplenet.com, freebsd-current@FreeBSD.ORG Subject: Re: Download of FreeBSD 3.0-SNAP Message-ID: <27308.905841833@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 14 Sep 1998 17:29:30 CDT." <199809142229.RAA09230@detlev.UUCP>
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In message <199809142229.RAA09230@detlev.UUCP>, Joel Ray Holveck writes: >> 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. > >I would guess (and this is a guess, feel free to correct) that it's >still fairly good, if it simply is performing an elevator sort keyed >on block numbers. I would expect that most translations leave the >order of the blocks alone. (ie, if block n is closer to the spindle >than n+1, then both are closer than n+2, assuming a spiral instead of >an actual CHS. Latency is still an issue, but not much.) This would >mean that such a sort would still be 100% valid. Well, this is almost still the case. Most modern disks lay out the sectors in a track backwards, they start reading as soon as they hit the track and cache all they get. That means that if you ask for sector 5, there is a good likelyhood that 6, 7, 8... is already in the cache when you ask for them a moment later. -- Poul-Henning Kamp FreeBSD coreteam member phk@FreeBSD.ORG "Real hackers run -current on their laptop." "ttyv0" -- What UNIX calls a $20K state-of-the-art, 3D, hi-res color terminal To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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