Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!ncrlnk!ncr-mpd!Chuck.Phillips From: Chuck.Phillips@FtCollins.NCR.COM (Chuck.Phillips) Newsgroups: comp.benchmarks Subject: Re: Measuring disk read times for Unix Message-ID: Date: 4 Mar 91 16:30:54 GMT References: <714@opus.NMSU.Edu> <1991Feb27.233049.2972@intellistor.com> Sender: uucp@ncr-mpd.FtCollins.NCR.COM Distribution: comp Organization: NCR Microelectronics, Ft. Collins, CO Lines: 26 In-reply-to: taylor@intellistor.com's message of 27 Feb 91 23:30:49 GMT In article <714@opus.NMSU.Edu> pfeiffer@nmsu.edu (Joe Pfeiffer) writes: Joe>In order to measure write times, I'm using the O_SYNC to flush my data Joe>to disk on each write. So far so good. Joe> Joe>I'm having trouble trying to do the equivalent for reads... >>>>> On 27 Feb 91 23:30:49 GMT, taylor@intellistor.com (Dick Taylor) said: Dick> There are a number of ways to do it. The niftiest that I ever found was Dick> to use the mount() and unmount() system calls to unmount the filesystem Dick> between each iteration of the benchmark. On the nose, Dick. SVr4 and SunOS use a lazy pageout method; a file mapped into memory is mapped out (LRU) only if there is a request for more memory _and_ there is no unallocated RAM (and umounts, of course). Theoretically, a system with lots of excess RAM may leave a a file paged into RAM indefinitely. I suspect the same is true of OSF/1. Anyone in the know care to comment? "Sticky bits? We don't need no stinkin' sticky bits!" -- M.E. :-) Cheers, -- Chuck Phillips MS440 NCR Microelectronics chuck.phillips%ftcollins.ncr.com 2001 Danfield Ct. Ft. Collins, CO. 80525 ...uunet!ncrlnk!ncr-mpd!chuck.phillips