From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Sun, 27 Jul 2003 06:27:45 -0600 From: Grant Grundler To: Carlos O'Donell Cc: Matthew Wilcox , parisc-linux@parisc-linux.org Subject: Re: [parisc-linux] Generic light-weight syscall. Message-ID: <20030727122745.GC16753@dsl2.external.hp.com> References: <20030725063739.GA13017@systemhalted> <20030725113700.GH1485@parcelfarce.linux.theplanet.co.uk> <20030726174845.GF31744@systemhalted> <20030726180031.GG31744@systemhalted> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <20030726180031.GG31744@systemhalted> Sender: parisc-linux-admin@lists.parisc-linux.org Errors-To: parisc-linux-admin@lists.parisc-linux.org List-Help: List-Post: List-Subscribe: , List-Id: parisc-linux developers list List-Unsubscribe: , List-Archive: On Sat, Jul 26, 2003 at 02:00:32PM -0400, Carlos O'Donell wrote: > Talked to Rik Van Riel about fast gettimeofday and he indicated that > it's not doable since you can't guarantee your process will get > scheduled on another CPU whose clock is out of sync by more than X and > get negative time. Yes we can. We can sync CR16 across CPUs within a few CPU cycles. I've described this before on parisc-linux. "sync" means figure out the difference between CR16 on several CPUs and using CPU 0 as the reference. > Though I imagine you were talking about having one > CPU update one page with time on it... and then other CPU's read this? > LaMont notes that there is no requirement from the PA design that CPU's > clock at _exactly_ the same frequency or have monotonically incrementing > clocks at the right rate. correct. IIRC 9000/870 have seperate clock sources. But all the boxes we support to date have exactly one clock source. The multi-cell boxes (like superdome) will have multiple sources and I don't know how to handle those - maybe a "not quite so fast" gettimeofday(). hth, grant