From owner-freebsd-hackers Wed Feb 17 12: 3:39 1999 Delivered-To: freebsd-hackers@freebsd.org Received: from iquest3.iquest.net (iquest3.iquest.net [209.43.20.203]) by hub.freebsd.org (Postfix) with SMTP id F1BA010EAD for ; Wed, 17 Feb 1999 12:03:36 -0800 (PST) (envelope-from toor@y.dyson.net) Received: (qmail 13504 invoked from network); 17 Feb 1999 20:03:34 -0000 Received: from dyson.iquest.net (HELO y.dyson.net) (198.70.144.127) by iquest3.iquest.net with SMTP; 17 Feb 1999 20:03:34 -0000 Received: (from root@localhost) by y.dyson.net (8.9.1/8.9.1) id PAA70095; Wed, 17 Feb 1999 15:03:34 -0500 (EST) Message-Id: <199902172003.PAA70095@y.dyson.net> Subject: Re: vm_page_zero_fill In-Reply-To: <199902171858.LAA21748@usr07.primenet.com> from Terry Lambert at "Feb 17, 99 06:58:38 pm" To: tlambert@primenet.com (Terry Lambert) Date: Wed, 17 Feb 1999 15:03:34 -0500 (EST) Cc: dyson@iquest.net, tlambert@primenet.com, toasty@home.dragondata.com, mike@smith.net.au, hackers@FreeBSD.ORG From: "John S. Dyson" Reply-To: dyson@iquest.net X-Mailer: ELM [version 2.4ME+ PL38 (25)] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG Terry Lambert said: > > > This is robbing Peter to pay Paul; in a way. The base assumption > > > that you are hiding is that you aren't constrained by memory > > > bandwidth. This isn't true if you are nearly saturating a PCI > > > bus with 4 BT848's (to pick the highest memory bandwidth application > > > I know about). > > > > Prezeroing doesn't take any significant CPU if there are no cycles > > available. It does increase latency slightly, if zeroing is allowed > > to happen. > > He's strapped on memory bandwidth, not CPU cycles. He's willing to > eat zeroing on in those cases where he has no choice because it > impacts base functionality. > If zeroing isn't allowed to happen, then there'll be no additional bandwidth used. > > > > The prezeroing isn't adding any cost to him, the ability to support > > returning non-initialized data from the kernel would be useful. In > > that case, turning off prezeroing *might* help (but probably won't.) > > Again, he's wanting to reclaim memory bandwidth from the prezeroing > of pages that are prezeroed not because they need to be, but for > security reasons that he doesn't care about. > That really doesn't make any (much) difference. Turning off prezeroing is easy anyway (sysctl.) -- John | Never try to teach a pig to sing, dyson@iquest.net | it makes one look stupid jdyson@nc.com | and it irritates the pig. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message