Re: kernel thread as real threads..

Scott Long <scottl@xxxxxxxxxx> · Fri, 20 Jan 2006 02:19:34 -0700

Gleb Smirnoff wrote:
On Fri, Jan 20, 2006 at 01:19:55AM -0500, Kris Kennaway wrote:

K> > the example I showed was the 'ps' from ddb which of course doesn't show 
K> > any stats anyhow.

K> 
K> Yeah, I know that, but they're also not displayed in ps(1) or top(1),

K> etc.
And this is a serious issue, that is present in our last releases. If a
was a newbie installing FreeBSD for first time, this fact will hurt my
impression about operating system most.

For KSE, threads are just a figment of the imagination of the kernel.  A 
thread that

the kernel sees has no specific correlation to a thread that exists in 
an application.

Trying to associate stats with these threads is absolultely meaningless. 
 The

processing time accumulated for a particular thread that the kernel sees 
could well

be the aggregate of a number of user threads, and those user threads are 
likely migrating

between the kernel threads.  That's the whole point of M:N threading 
=-)  Saying that

thread 1 did X amount of work and thread 2 did Y amount of work simply 
has no meaning,

other than that the parent process did X+Y amount of work.
For 1:1 threading is does make a little more sense.  We'd have to come 
up with a way

to accurately express whether the thread accounting stats are meaningful 
or not depending

on which library is in use.  Adding to the complexity would be that KSE 
can create system

and process scope threads, and that system scope threads behave mostly 
like 1:1 threads.

If someone wants to tackle all of this, that would be great, but my only 
request would be

that it can't sacrifice clarity in one library over another library.
Scott
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Re: kernel thread as real threads..

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