Subject: Re: tsleep
To: Mirian Crzig Lennox <>
From: Jason Thorpe <>
List: tech-kern
Date: 07/06/1999 11:48:34
On 06 Jul 1999 14:31:15 -0400 
 Mirian Crzig Lennox <> wrote:

 > > Um... It's NOT "two distinct symbol tables".
 > In most cases, it really is.  For example, in /sys/kern/vfs_subr.c we
 > have
 > In vinvalbuf():
 >     tsleep((caddr_t)bp, slpflag | (PRIBIO + 1), "vinvalbuf",lptimeo);
 > In vflushbuf():
 >     tsleep((caddr_t)&vp->v_numoutput, PRIBIO + 1, "vflushbuf", 0);
 > In vget():
 >     tsleep((caddr_t)vp, PINOD, "vget", 0);
 > In vgone():
 >     tsleep((caddr_t)vp, PINOD, "vgone", 0);
 > In effect, we're duplicating information that already exists in the
 > kernel symbol table.

The point is that tsleep() is more flexible than that.  What if you sleep
in two different places in the same function, and want to differentiate?

 > If tsleep() were changed such that the calls could be:
 >     tsleep((caddr_t)bp, slpflag | (PRIBIO + 1), (caddr_t)vinvalbuf,lptimeo);
 > etc.,
 > Then we'd get back 27 bytes "for free".  Maybe not a lot, but why
 > waste any space if you don't need to?  And in the aggregate, it could
 > easily be a few K of kernel mem.

The "savings" is a lot less important when you consider that:

	(1) Constant strings are placed into the .text or .rodata
	    sections (.rodata lets loaded w/ .text).

	(2) That combined section is always rounded to a page
	    size anyhow.

...this "savings" would have to be *considerable* to even consider
throwing away the (sometimes very very very very useful when debugging)
flexibility that having that wchan message provides.

        -- Jason R. Thorpe <>