Date: Sat, 06 Dec 2008 20:23:44 -0700 (MST) From: "M. Warner Losh" <imp@bsdimp.com> To: kostikbel@gmail.com Cc: svn-src-head@FreeBSD.org, rdivacky@FreeBSD.org, src-committers@FreeBSD.org, svn-src-all@FreeBSD.org Subject: Re: svn commit: r185647 - in head/sys: kern sys Message-ID: <20081206.202344.-160243400.imp@bsdimp.com> In-Reply-To: <20081205230002.GX2038@deviant.kiev.zoral.com.ua> References: <200812052050.mB5KoOcV072648@svn.freebsd.org> <20081205224600.GA16948@freebsd.org> <20081205230002.GX2038@deviant.kiev.zoral.com.ua>
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In message: <20081205230002.GX2038@deviant.kiev.zoral.com.ua>
Kostik Belousov <kostikbel@gmail.com> writes:
: 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.
Is that a measurable good difference, or a measurable bad difference?
Warner
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