Date: Wed, 17 Feb 1999 16:39:30 -0500 (EST) From: "John S. Dyson" <dyson@iquest.net> To: tlambert@primenet.com (Terry Lambert) Cc: dyson@iquest.net, tlambert@primenet.com, toasty@home.dragondata.com, mike@smith.net.au, hackers@FreeBSD.ORG Subject: Re: vm_page_zero_fill Message-ID: <199902172139.QAA70278@y.dyson.net> In-Reply-To: <199902171838.LAA20158@usr07.primenet.com> from Terry Lambert at "Feb 17, 99 06:38:39 pm"
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Terry Lambert said: > > > The thing that appalled me was what you said about BSS being zero'ed > > > in the kernel space using zeroed pages instead of as a result of an > > > explicit zeroing by the execution class loader. > > > > That is the way that it works. Explict zeroing is wasteful because > > it cannot easily take advantage of background prezeroing... However, > > recently prezeroed pages make for efficient usage of cache. The zero > > queue (and all others) are designed to take advantage of recent cache > > usage. > > 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). > I just realized something: Memory bandwidth is >> PCI bandwidth on good designs. I believe that the PCI and memory busses are decoupled on at least some X86 machines. -- 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
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