Date: Sun, 7 Dec 2008 12:26:20 +0200 From: Kostik Belousov <kostikbel@gmail.com> To: "M. Warner Losh" <imp@bsdimp.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: <20081207102620.GK2038@deviant.kiev.zoral.com.ua> In-Reply-To: <20081206.202344.-160243400.imp@bsdimp.com> References: <200812052050.mB5KoOcV072648@svn.freebsd.org> <20081205224600.GA16948@freebsd.org> <20081205230002.GX2038@deviant.kiev.zoral.com.ua> <20081206.202344.-160243400.imp@bsdimp.com>
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--9SzJfJEKNI6APITJ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Dec 06, 2008 at 08:23:44PM -0700, M. Warner Losh wrote: > 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 > : > >=20 > : > > Log: > : > > Several threads in a process may do vfork() simultaneously. Then,= all > : > > parent threads sleep on the parent' struct proc until correspondi= ng > : > > child releases the vmspace. Each sleep is interlocked with proc m= utex of > : > > the child, that triggers assertion in the sleepq_add(). The asser= tion > : > > requires that at any time, all simultaneous sleepers for the chan= nel use > : > > the same interlock. > : > > =20 > : > > Silent the assertion by using conditional variable allocated in t= he > : > > child. Broadcast the variable event on exec() and exit(). > : > > =20 > : > > 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(). > : >=20 > : > are there any differences (performance etc.) in using condition varia= bles > : > instead of sleep/wakeup? > :=20 > : 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. > :=20 > : Would I been able to convert _all_ uses of the struct proc * wait chann= el > : to cond vars operation, this may be measurable on some loads, since it > : would exclude spurious wakeups. >=20 > Is that a measurable good difference, or a measurable bad difference? I expect this could be measurable good difference, i.e. such patch might improve performance on some loads by eliminating false wakeups. --9SzJfJEKNI6APITJ Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (FreeBSD) iEYEARECAAYFAkk7pMsACgkQC3+MBN1Mb4iETgCfX2qVnP2e+1gPG2HBrwspv+HV EtoAoMuhcsgY0JbRg3gnuTQ3zvSmU0Af =jhP7 -----END PGP SIGNATURE----- --9SzJfJEKNI6APITJ--
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