svn commit: r206497 - in head: sbin/geom/class sbin/geom/class/sched sys/geom/sched sys/modules/geom sys/modules/geom/geom_sched sys/modules/geom/geom_sched/gs_sched sys/modules/geom/geom_sched/gsc...

[Luigi Rizzo]

[Cc-ing Fabio as he may have more details]

On Wed, Apr 14, 2010 at 09:46:17AM +0200, Pawel Jakub Dawidek wrote:
> On Mon, Apr 12, 2010 at 11:05:12PM +0200, Luigi Rizzo wrote:
> > On Mon, Apr 12, 2010 at 10:49:26PM +0200, Pawel Jakub Dawidek wrote:
> > ...
> > > > @@ -0,0 +1,19 @@
> > > > +# GEOM_LIBRARY_PATH
> > > > +# $FreeBSD$
> > > > +
> > > > +.PATH: /usr/src/sbin/geom/misc
> > > > +
> > > > +CFLAGS += -I/usr/src/sbin/geom
> > > 
> > > This doesn't look right.
> > 
> > probably a leftover from older versions of this code for 6.x .
> > I will do more tests tomorrow (for 7.x at this point, there is
> > no point in trying to support 6.x I believe) and try to remove
> > it if not necessary.
> 
> As Rui said you should use ${.CURDIR} instead of hardcoding /usr/src/.

I thought i already fixed this yesterday.

> BTW. So you decided to implement insert/remove functionality after all.
> I have some questions:
> 
> - It is implemented as internal gsched hack, which is a pity, because
>   this might be very useful functionality for other classes in the future.
>   Is there a plan to make it more general and move it to the GEOM itself?

yes there is such a plan -- of course if nobody has objections.
In principle it is only a library extensions with no modifications
to geom internals.

However, when we developed that last year, we hit some corner case
where removal of an active node causes either a race or (if you try
to protect from the race) a livelock. Fixing this may require some
small cleanup to geom internals (we discusses the issue with phk
at last EuroBSDCon. Fabio may give you more details, as far as i
remember the problem was that some geom code takes shortcuts instead
of following a chain of pointers, and this can end up in the wrong
place in case of a removal.)

For this reason, at this time i am not recommending to remove a
node from a chain with outstanding transactions until the issue is solved.

> - Why g_sched_flush_pending() operates on global structure? I think it
>   will break if you try to insert and remove at the same time.

i need to check this.

cheers
luigi