Date: Fri, 2 Oct 2009 10:29:50 -0700 (PDT) From: Richard Mahlerwein <mahlerrd@yahoo.com> To: freebsd-performance@freebsd.org Subject: Re: A specific example of a disk i/o problem Message-ID: <160343.45338.qm@web51006.mail.re2.yahoo.com>
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>From: Dieter <freebsd@sopwith.solgatos.com> >Subject: Re: A specific example of a disk i/o problem >To: freebsd-performance@freebsd.org >Date: Friday, October 2, 2009, 1:07 AM > >Updated demo, just to make sure: > ># big_file is larger than main memory, on same disk as man (/usr) >time man de >cat big_file > /dev/null >cat big_file > /dev/null & >time man de Trying it on something that surely will have i/o issues: PIII 500 w/ 60 GB PATA drive and 256 MB RAM. Blank minimal install + man pages right now. I'm trying with a "file /etc/" command instead of trying to reliably time man... It seems the file command always hits the disk. This should also make any sort of "flushing" unecessary, shouldn't it? Anyway, I tried it with the man command but couldn't discern any difference at all with it, so I'm repeating with "file" which at least gives SOME variance. liebnitz# uname -a FreeBSD xyz 7.2-RELEASE FreeBSD 7.2-RELEASE #0: Fri May 1 08:49:13 UTC 2009 root@walker.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC i386 liebnitz# time dd if=/dev/zero of=/usr/bigfile count=4096 bs=1M 4096+0 records in 4096+0 records out 4294967296 bytes transferred in 363.700967 secs (11809062 bytes/sec) 0.055u 83.971s 6:03.78 23.0% 25+1071k 128+34391io 0pf+0w liebnitz# time file /etc/ [run 5 times] 4.052u 0.047s 0:04.14 98.7% 15+1085k 0+0io 0pf+0w 4.068u 0.031s 0:04.13 99.0% 16+1095k 0+0io 0pf+0w 4.052u 0.046s 0:04.13 99.0% 16+1101k 0+0io 0pf+0w 4.044u 0.054s 0:04.13 99.0% 16+1092k 0+0io 0pf+0w 4.052u 0.046s 0:04.13 99.0% 15+1091k 0+0io 0pf+0w Ok, so that looks pretty repeatable. Now... liebnitz# cat /usr/bigfile > /dev/null & [1] 37923 liebnitz# time file /etc/* [again run 5 times] 4.146u 0.038s 0:06.80 61.3% 15+1103k 87+0io 8pf+0w 4.128u 0.054s 0:06.73 61.9% 15+1095k 93+0io 6pf+0w 4.127u 0.056s 0:06.65 62.7% 14+1058k 88+0io 4pf+0w 4.111u 0.072s 0:06.84 61.1% 15+1049k 91+0io 6pf+0w 4.115u 0.066s 0:06.86 60.7% 15+1022k 91+0io 6pf+0w BTW, after the cat is done... liebnitz# time file /etc/* 4.051u 0.047s 0:04.13 99.0% 15+1078k 0+0io 0pf+0w I see no unexpected issues, only a minor slowdown, and that could be processer contention, IMO. (Sorry for duplicate, I was rewriting with the change to "file" instead of "man" and the two year old decided to press some keys and sent the message.)
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