svn commit: r185647 - in head/sys: kern sys

[Kostik Belousov]

On Fri, Dec 05, 2008 at 11:46:00PM +0100, Roman Divacky wrote:
> On Fri, Dec 05, 2008 at 08:50:24PM +0000, Konstantin Belousov wrote:
> > Author: kib
> > Date: Fri Dec  5 20:50:24 2008
> > New Revision: 185647
> > URL: http://svn.freebsd.org/changeset/base/185647
> > 
> > Log:
> >   Several threads in a process may do vfork() simultaneously. Then, all
> >   parent threads sleep on the parent' struct proc until corresponding
> >   child releases the vmspace. Each sleep is interlocked with proc mutex of
> >   the child, that triggers assertion in the sleepq_add(). The assertion
> >   requires that at any time, all simultaneous sleepers for the channel use
> >   the same interlock.
> >   
> >   Silent the assertion by using conditional variable allocated in the
> >   child. Broadcast the variable event on exec() and exit().
> >   
> >   Since struct proc * sleep wait channel is overloaded for several
> >   unrelated events, I was unable to remove wakeups from the places where
> >   cv_broadcast() is added, except exec().
> 
> are there any differences (performance etc.) in using condition variables
> instead of sleep/wakeup?

I do not think that there is any measurable difference. On the other
hand, the patch makes struct proc bigger by int + pointer. This shall
not be a problem too.

Would I been able to convert _all_ uses of the struct proc * wait channel
to cond vars operation, this may be measurable on some loads, since it
would exclude spurious wakeups.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 195 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/svn-src-head/attachments/20081205/a6f61ae1/attachment.pgp