Date: Sat, 14 Feb 2009 07:33:25 -0700 From: Scott Long <scottl@samsco.org> To: Ivan Voras <ivoras@freebsd.org> Cc: freebsd-current@freebsd.org, freebsd-stable@freebsd.org Subject: Re: HEADS UP: Major CAM performance regression Message-ID: <4996D635.3000802@samsco.org> In-Reply-To: <9bbcef730902131421r53efa13dq371658888747f387@mail.gmail.com> References: <499551B9.7050805@samsco.org> <gn3ssi$j1r$1@ger.gmane.org> <4995DFE5.1020205@samsco.org> <9bbcef730902131421r53efa13dq371658888747f387@mail.gmail.com>
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Ivan Voras wrote: > 2009/2/13 Scott Long <scottl@samsco.org>: >> Ivan Voras wrote: >>> Scott Long wrote: >>> >>>> 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. >>> I notice that write performance on an ESXi 3.5 hosted system is doubled, >>> but read performance remains the same (in bonnie++). >>> On a CISS system there is no significant change. >> bonnie is an unreliable tool for measuring performance. > > I'll try your suggestion if you have one. I don't have a magic universal testing suite in my back pocket, sorry. You need to look at your expected workload and develop tests to simulate it. When I do testing during driver development, I try a lot of different parallel, sequential, large i/o, and small i/o combinations. > > (except if it's about bonnie++ primarily measuring sequential > read/write - if a system can't do sequential IO well, it probably > won't do random IO well) This is completely false. Disks can't do sequential i/o very well due to the physical limits of long seek times, but those seek times can be greatly amortized, even in a random workload, with tagged queueing and parallel dispatch from the OS. Bonnie simply cannot exercise this very well. Bonnie tests system latency for discrete I/O's. That is all it tests. Scott
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