Date: Fri, 13 Feb 2009 13:43:17 -0700 From: Scott Long <scottl@samsco.org> To: Tom Evans <tevans.uk@googlemail.com> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: HEADS UP: Major CAM performance regression Message-ID: <4995DB65.5020200@samsco.org> In-Reply-To: <1234531085.2998.42.camel@localhost> References: <499551B9.7050805@samsco.org> <1234531085.2998.42.camel@localhost>
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Tom Evans wrote: > On Fri, 2009-02-13 at 03:55 -0700, Scott Long wrote: >> All, >> >> A major performance regression was introduced to the CAM subsystem in >> FreeBSD 7.1. The following configurations are known to be affected: >> >> VMWare ESX >> VMWare Fusion >> (using bt or lsilogic controller options) >> HP CISS RAID >> Some MPT-SAS combinations with SATA drives attached >> (Includes Dell SAS5/ir, but not PERC5/PERC6). >> >> Pure SCSI and SAS subsystems likely are NOT affected. Any hardware >> that uses the 'ata' driver is also definitely NOT affected. To >> determine if your installation is affected, run the following command as >> root: >> >> camcontrol tags da0 >> >> Substitute 'da0' with another appropriate drive device number, if >> needed. Note that this ONLY AFFECTS 'da' DEVICES. If your disks are >> 'ad' devices, they are NOT affected. >> >> The result from running this command should be an output similar to the >> following: >> >> (pass0:mpt0:0:8:0): device openings: 255 >> >> If, instead, it reports a value of '1', you are likely affected. Note >> that it may be normal for USB memory devices to report a low number. >> Also, many legacy SCSI disks, and devices that are not disks, may also >> be expected to report a low number. >> >> The effect of this problem is that only one I/O command will be issued >> to the controller and disk at a time, instead of overlapping multiple >> commands in parallel. This causes significantly higher latency in >> servicing moderate and heavy I/O workloads, leading to very poor >> performance. Performance can be easily compared by downgrading to >> FreeBSD 7.0. >> >> I have committed a fix for this problem for FreeBSD 8-CURRENT as of SVN >> revision 188570. FreeBSD 7-STABLE will be updated with the fix in a few >> days once I've gotten confirmation that the fix works and doesn't cause >> any adverse side-effects. Anyone wanting to help in this validation >> effort should apply the attached patch to their kernel source tree and >> recompile. Please contact me directly by email to report if the problem >> is fixed for you. >> >> If the validation process goes smoothly, I will work with the release >> engineering team to turn this fix into an official errata update for >> FreeBSD 7.1. >> >> Thanks in advance for your help. >> >> Scott >> > > Hi Scott > > I have one da0 device, a USB attached hard disk: > > umass0: <LaCie LaCie Hard Drive USB, class 0/0, rev 2.00/0.00, addr 2> > on uhub6 > da0 at umass-sim0 bus 0 target 0 lun 0 > da0: <SAMSUNG SP2514N VF10> Fixed Direct Access SCSI-2 device > da0: 40.000MB/s transfers > da0: 238475MB (488397168 512 byte sectors: 255H 63S/T 30401C) > > > camcontrol shows: > >> $ sudo camcontrol tags da0 > (pass0:umass-sim0:0:0:0): device openings: 1 > > Is that to be expected? This is RELENG_7 from October '08: > The date falls within the range. Have you tried the patch to see if it changes anything? Scott
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