Date: Wed, 18 Feb 2009 09:11:51 +0100 From: Gary Jennejohn <gary.jennejohn@freenet.de> To: Scott Long <scottl@samsco.org> Cc: FreeBSD Current <freebsd-current@FreeBSD.org>, Stable <freebsd-stable@FreeBSD.org>, Bruce Evans <brde@optusnet.com.au>, scsi@FreeBSD.org Subject: Re: HEADS UP: More CAM fixes. Message-ID: <20090218091151.4d9c2bd7@ernst.jennejohn.org> In-Reply-To: <499B221C.2050804@samsco.org> References: <499981AF.9030204@samsco.org> <20090217164203.4c586f48@ernst.jennejohn.org> <20090218073542.E5200@delplex.bde.org> <499B221C.2050804@samsco.org>
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On Tue, 17 Feb 2009 13:46:20 -0700 Scott Long <scottl@samsco.org> wrote: > Bruce Evans wrote: > > On Tue, 17 Feb 2009, Gary Jennejohn wrote: > > > >> I tested this with an Adaptec 29160. I saw no real improvement in > >> performance, but also no regressions. > >> > >> I suspect that the old disk I had attached just didn't have enough > >> performance reserves to show an improvement. > >> > >> My test scenario was buildworld. Since /usr/src and /usr/obj were both > >> on the one disk it got a pretty good workout. > > ^^^^ low > >> > >> AMD64 X2 (2.5 GHz) with 4GB of RAM. > > > > Buildworld hardly uses the disk at all. It reads and writes a few hundred > > MB. Ideally the i/o should go at disk speeds of 50-200MB/S and thus take > > between 20 and 5 seconds. In practice, it will take a few more seconds. > > physically but perhaps even less virtually due to parallelism. > > > > Bruce > > Yes, on modern machines, buildworld is bound almost completely by disk > latency, and not at all by disk or controller bandwidth. > > Scott > Maybe I misunderstood something, but I thought the patch was supposed to improve queuing. Seems like all the seeks during a buildowrld would exercise that. All I can say is that the disk did _lots_ of seeking. --- Gary Jennejohn
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