Date: Sat, 8 Apr 1995 09:47:37 -0700 (PDT) From: "Rodney W. Grimes" <rgrimes@gndrsh.aac.dev.com> To: taob@gate.sinica.edu.tw (Brian Tao) Cc: freebsd-current@FreeBSD.org Subject: Re: Disk performance Message-ID: <199504081647.JAA15531@gndrsh.aac.dev.com> In-Reply-To: <Pine.BSI.3.91.950408171607.787F-100000@aries.ibms.sinica.edu.tw> from "Brian Tao" at Apr 8, 95 05:34:02 pm
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> > On Sat, 8 Apr 1995, Rodney W. Grimes wrote: ... > > Yes, IDE drives load the cpu down far more, as they not only have to > > bcopy the bytes to and from user land, they also have to bcopy them > > to and from the disk. > > I presume that EIDE drives and drivers that support DMA wouldn't > suffer from this particular deficiency then. Sorry, I don't mean to > pick your brains in public like this. I hope someone else is learning > the basics of disk transfer too. :) EIDE drives that support mode 2 DMA would not suffer from this problem if the FreeBSD drives also supported mode 2 DMA. ... > > Especially with out detailed information about how the kernel implements > > the buffer copies to and from user land. I'm pretty sure the SGI boxes > > use page flipping, > > Hmmm, the only page flipping I know of is a double-buffered > animation technique used on the Apple II hi-res graphics screen. :) Same concept, different use. Basically you swap the users buffer for a kernel buffer by bit flipping in the vm system, this saves the bcopy operation, just like it does for graphics page flipping. -- Rod Grimes rgrimes@gndrsh.aac.dev.com Accurate Automation Company Custom computers for FreeBSD
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