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.
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