Date: Wed, 20 Dec 2006 14:05:44 +1300 From: Mark Kirkwood <markir@paradise.net.nz> To: freebsd-stable@freebsd.org Subject: Cached file read performance with 6.2-PRERELEASE Message-ID: <45888C68.10305@paradise.net.nz>
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In the process of investigating performance in another area I happened to be measuring sequential cached reads (in a fairly basic manner): $ dd if=/dev/zero of=/tmp/file bs=8k count=100000 # create file 819200000 bytes transferred in 4.849394 secs (168928321 bytes/sec) $ dd of=/dev/null if=/tmp/file bs=8k # read it 819200000 bytes transferred in 2.177922 secs (376138354 bytes/sec) $ dd of=/dev/null if=/tmp/file bs=8k # read again 819200000 bytes transferred in 2.178407 secs (376054620 bytes/sec) $ dd of=/dev/null if=/tmp/file bs=32k # read it 819200000 bytes transferred in 1.801944 secs (454620117 bytes/sec) I ran vmstat to check there really was no read access to the filesystem. Now I had no idea whether this was the sort of performance to be expected or not, so checked on an *identical* cpu, memory, mobo machine running Gentoo - this gets 620MB/s for 8k blocks and 700MB/s for 32k ones. I'm gonna quickly add - it's not my intention to start a Linux vs BSD war here, the Gentoo data is mentioned to suggest that "Well - looks like I should see if I can get the BSD box to do more than 433MB/s!". The system is 2x1.26Ghz PIII, Supermicro P3TDER Serverworks HE-SL (dual channel), 2x1G PC133 ECC DIMMS FreeBSD setup is: FreeBSD 6.2-PRERELEASE #7: Mon Nov 27 19:32:33 NZDT 2006, with kernel based on GENERIC + SMP. I have /etc/malloc.conf -> >aj Any suggestions/ideas about how to improve this? Cheers Mark P.s: Someone's gonna say this "why does this unrealistic test matter?". Well, I work with databases a lot (usually postgres) and a great deal of effort goes into caching table/relation data as much as possible - so reading (and writing - but I'm not testing that here!) it as fast as possible (sequentially or random) is clearly important!
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