Date: Sat, 14 Feb 2009 18:14:27 +0100 From: "Svein Skogen (listmail account)" <svein-listmail@stillbilde.net> To: Scott Long <scottl@samsco.org> Cc: FreeBSD Current <freebsd-current@freebsd.org>, FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: HEADS UP: Major CAM performance regression Message-ID: <4996FBF3.3040801@stillbilde.net> In-Reply-To: <499551B9.7050805@samsco.org> References: <499551B9.7050805@samsco.org>
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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.
Any estimate on when this will be MFC'ed down to RELENG_7 yet?
//Svein
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