Subject: Re: partition bookkeeping
To: None <email@example.com>
From: der Mouse <mouse@Rodents.Montreal.QC.CA>
Date: 09/26/1999 23:31:44
> Let me guess, using fsck as an example:
> fsck gets "/dev/disk/rsd2d" as its device
> fsck calls open("/dev/disk/rsd2d") CS #1
> Eventually the vnode gets resolved, and
> the open routine for the vnode goes
> out to userland to talk to this daemon
> which handles all the device mappings CS #2
Whoa. I think this is the first time anyone has even suggested that
userland would be involved on *every open*. Some schemes have a
userland program that shoves wedge info into the kernel and dies; some
have a daemon that notices new disks appearing and does something
useful with them. Some have both. But I don't think I've seen
anything that doesn't even load the wedge info into the kernel.
> Microkernels don't work -- context switching is not cheap.
Why don't microkernels work? Too expensive - all those context
Why are context switches expensive? Because they happen
rarely, so nobody bothers to optimize them.
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