Date: Mon, 24 Apr 2006 19:24:14 -0400 From: Alexander Kabaev <kabaev@gmail.com> To: Julian Elischer <julian@elischer.org> Cc: Kirk McKusick <mckusick@McKusick.COM>, arch@freebsd.org, John-Mark Gurney <gurney_j@resnet.uoregon.edu> Subject: Re: Linus Torvalds on FreeBSD's Use of Copy-on-write Message-ID: <20060424192414.0dbaa534@kan.dnsalias.net> In-Reply-To: <444C765B.7070803@elischer.org> References: <200604240633.k3O6XUJ0042841@chez.mckusick.com> <20060424064352.GA728@funkthat.com> <444C765B.7070803@elischer.org>
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[-- Attachment #1 --] On Sun, 23 Apr 2006 23:55:23 -0700 Julian Elischer <julian@elischer.org> wrote: > John-Mark Gurney wrote: > > >Kirk McKusick wrote this message on Sun, Apr 23, 2006 at 23:33 -0700: > > > > > >>Linus explained that while this may look good on specific > >>benchmarks, it actually introduces extra overhead, "the thing is, > >>the cost of > >> > >> > > > >Has he benchmarked this to prove his point? And has he done it over > >realworld work loads, like Apache or another "standard" program > >instead of a microbenchmark designed especially to make COW look bad? > > > > > > Well no-one has even confirmed that freeBSD does all this > "page flipping" etc. I doubt that Linus has looked inside the BSD > kernels. He's probably just repeating what he's been told, and that's > so accurate, right? > > I know that freeBSD developers have over the last few years also > acknowledged that > the speed of modern CPUs vs. memeory speeds makes it often less > efficient to do certain optimisations than it used to be. > > > > > >As w/ all theories, w/o numbers, they are only theories till backed > >up w/ benchmarks. > > > >This isn't suppose to defend COW, but it is designed to ensure that > >people don't stop exploring just because someone says something... > > > > > > > _______________________________________________ > freebsd-arch@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-arch > To unsubscribe, send any mail to > "freebsd-arch-unsubscribe@freebsd.org" The original zero-copy code was used to stream network data directly to an onboard SDRAM memory on an extension PCI card. Linus' notes about relative cost of memory-to-memory copies vs. TLB shootdowns and possible page access traps had little relevance there. -- Alexander Kabaev -- Alexander Kabaev [-- Attachment #2 --] -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.2.2 (FreeBSD) iD8DBQFETV4nQ6z1jMm+XZYRAmb0AJ9wJUar/mwUJc7XwoCbcfTNR5j6WgCgn6xu HNu/4H0KgHUFtuWcyiXutpw= =MBNK -----END PGP SIGNATURE-----help
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