Date: Sat, 14 Feb 2009 16:44:47 +0100 From: Ivan Voras <ivoras@freebsd.org> To: Scott Long <scottl@samsco.org> Cc: freebsd-current@freebsd.org, freebsd-stable@freebsd.org Subject: Re: HEADS UP: Major CAM performance regression Message-ID: <9bbcef730902140744i14c2a9e6i211a549eada7b057@mail.gmail.com> In-Reply-To: <4996D635.3000802@samsco.org> References: <499551B9.7050805@samsco.org> <gn3ssi$j1r$1@ger.gmane.org> <4995DFE5.1020205@samsco.org> <9bbcef730902131421r53efa13dq371658888747f387@mail.gmail.com> <4996D635.3000802@samsco.org>
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2009/2/14 Scott Long <scottl@samsco.org>: >> 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. Of course you're right about testing for specific workloads - I just thought you needed data points "from the field" if the patch is helping or not. >> (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 I don't follow this - where are the long seek times in sequential IO? > 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. Doesn't tagged queuing serve, among other things, to decrease overall latency for IOs? Since AFAIK UFS queues multiple IO requests in both directions (read-ahead and write-behind), shouldn't the benefits of the patch - liberating the tags - be visible even with sequential IO? I have the systems on which I tested for a few more days, if you need the data I can run some other tests (randomio?).
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