Date: Tue, 30 Apr 1996 22:54:18 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: koshy@india.hp.com (A JOSEPH KOSHY) Cc: hackers@freebsd.org, current@freebsd.org Subject: Re: lmbench IDE anomaly Message-ID: <199604301324.WAA21150@genesis.atrad.adelaide.edu.au> In-Reply-To: <199604301053.AA141971583@fakir.india.hp.com> from "A JOSEPH KOSHY" at Apr 30, 96 04:23:03 pm
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A JOSEPH KOSHY stands accused of saying: > > >> two simultaneous runs on the scsi disk ... > The performance degradation per process is around 2x which is to be expected. > The overall throughput is around the same as the single benchmark case. > > However when the same exercise is repeated with the IDE disk: ... > Here we see a 8x degradation per process; 4x in terms of total throughput. > > Is this to be expected, or am i doing something wrong here? The system was > otherwise idle during these tests. That's about right. The SCSI disk gets the chance to sort the I/O to suit itself, optimising its performance. The IDE disk only gets to look at one transaction at a time, so it's at the mercy of the disksorting code in the operating system. I don't know that FreeBSD's disksort stuff is terribly wonderful, but I'd happily stand corrected. > Koshy -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] Collector of old Unix hardware. "Where are your PEZ?" The Tick [[
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