Date: Thu, 15 Dec 2011 14:25:26 +0100 From: Stefan Esser <se@freebsd.org> To: Michael Larabel <michael.larabel@phoronix.com> Cc: FreeBSD Stable Mailing List <freebsd-stable@freebsd.org>, Current FreeBSD <freebsd-current@freebsd.org>, Michael Ross <gmx@ross.cx>, freebsd-performance@freebsd.org, "O. Hartmann" <ohartman@zedat.fu-berlin.de>, Jeremy Chadwick <freebsd@jdc.parodius.com> Subject: Re: Benchmark (Phoronix): FreeBSD 9.0-RC2 vs. Oracle Linux 6.1 Server Message-ID: <4EE9F546.6060503@freebsd.org> In-Reply-To: <4EE9C79B.7080607@phoronix.com> References: <4EE1EAFE.3070408@m5p.com> <CAJ-FndDniGH8QoT=kUxOQ%2BzdVhWF0Z0NKLU0PGS-Gt=BK6noWw@mail.gmail.com> <4EE2AE64.9060802@m5p.com> <4EE88343.2050302@m5p.com> <CAFHbX1%2B5PttyZuNnYot8emTn_AWkABdJCvnpo5rcRxVXj0ypJA@mail.gmail.com> <4EE933C6.4020209@zedat.fu-berlin.de> <CAPjTQNEJDE17TLH-mDrG_-_Qa9R5N3mSeXSYYWtqz_DFidzYQw@mail.gmail.com> <20111215024249.GA13557@icarus.home.lan> <4EE9A2A0.80607@zedat.fu-berlin.de> <op.v6iv3qe5g7njmm@michael-think> <4EE9C79B.7080607@phoronix.com>
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Am 15.12.2011 11:10, schrieb Michael Larabel: > No, the same hardware was used for each OS. > > In terms of the software, the stock software stack for each OS was used. Just curious: Why did you choose ZFS on FreeBSD, while UFS2 (with journaling enabled) should be an obvious choice since it is more similar in concept to ext4 and since that is what most FreeBSD users will use with FreeBSD? Did you tune the ZFS ARC (e.g. vfs.zfs.arc_max="6G") for the tests? And BTW: Did your measured run times account for the effect, that Linux keeps much more dirty data in the buffer cache (FreeBSD has a low limit on dirty buffers since under realistic load the already cached data is much more likely to be reused and thus more valuable than freshly written data; aggressively caching dirty data would significantly reduce throughput and responsiveness under high load). Given the hardware specs of the test system, I guess that Linux accepts at least 100 times the dirty data in the buffer cache, compared to FreeBSD (where this number is at most in the tens of megabyte range). If you did not, then your results do not represent a server load (which I'd expect relevant, if you are testing against Oracle Linux 6.1 server), where continuous performance is required. Tests that run on an idle system starting in a clean state and ignoring background flushing of the buffer cache after the timed program has stopped are perhaps useful for a very lowly loaded PC, but not for a system with high load average as the default. I bet that if you compared the systems under higher load (which admittedly makes it much harder to get sensible numbers for the program under test) or with reduced buffer cache size (or raise the dirty buffer limit in FreeBSD accordingly, which ought to be possible with sysctl and/or boot time tuneables, e.g. "vfs.hidirtybuffers"). And a last remark: Single benchmark runs do not provide reliable data. FreeBSD comes with "ministat" to check the significance of benchmark results. Each test should be repeated at least 5 times for meaningful averages with acceptable confidence level. Regards, STefan
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