Date: Sat, 16 Oct 1999 13:54:18 +0200 (MET DST) From: Gerard Roudier <groudier@club-internet.fr> To: "Kenneth D. Merry" <ken@kdm.org> Cc: "Chris D. Faulhaber" <cdf.lists@fxp.org>, Andrew Gallatin <gallatin@cs.duke.edu>, scsi@FreeBSD.ORG Subject: Re: FreeBSD 3.2 / Slow SCSI Dell PowerEdge 4300 Message-ID: <Pine.LNX.3.95.991016133402.343A-100000@localhost> In-Reply-To: <199910152214.QAA52284@panzer.kdm.org>
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I have run some scenarii using multi-threaded IO streams under FreeBSD and result is that the overall performance results have been significantly better with tagged command queueing disabled. I used a Cheetah LVD and a DRVS LVD. What seems to happen when tagged command queuing is disabled, is that the IO scheduling policy can stay a long time (seconds) on one IO stream and then switch to another one, and so on ... This seem to be due (just guessing) to a side effect of the disksort algorithm that just makes the supposed multi-threaded IO streams become a succession of single-threaded IO streams that may each last seconds. If I am right (fill free to fix me if needed), it is actually the OS that might be inadequate for tagged command queuing benchmarking. Bug or feature ? ;-) G=E9rard.=20 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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