ntm1169@dsacg1.UUCP (Mott Given) (02/01/89)
I would like to know why the number of I/O's, as shown by "BLOCKS R/W"
in the BSD 4.3 accounting statistics, increases as the system workload
increases. I do not understand very much about UNIX internals, and
in other operating systems such as MVS one does not see the same
phenomenon.
Mott Given @ Defense Logistics Agency ,DSAC-TMP, Bldg. 27-1, P.O. Box 1605,
Systems Automation Center, Columbus, OH 43216-5002
UUCP: mgiven%dsacg1.uucp@daitc.arpa I speak for myself
Phone: 614-238-9431 AUTOVON: 850-9431
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Mott Given @ Defense Logistics Agency ,DSAC-TMP, Bldg. 27-1, P.O. Box 1605,
Systems Automation Center, Columbus, OH 43216-5002
UUCP: mgiven%dsacg1.uucp@daitc.arpa I speak for myself
Phone: 614-238-9431 AUTOVON: 850-9431dik@uva.UUCP (Casper H.S. Dik) (02/02/89)
In article <630@dsacg1.UUCP> ntm1169@dsacg1.UUCP (Mott Given) writes: > > I would like to know why the number of I/O's, as shown by "BLOCKS R/W" > in the BSD 4.3 accounting statistics, increases as the system workload > increases. I do not understand very much about UNIX internals, and > in other operating systems such as MVS one does not see the same > phenomenon. The 4.x manual getrusage(2) states: The numbers ru_inblock and ru_outblock acccount only for real i/o; data supplied by the cacheing machanism is charged only to the first process to read or write the data. [end of quote] (ru_inblock = number of fs input operations) (ru_outlock = number of fs output operations) So if you are on a lightly loaded system some blocks stay in the cache long enough to be used again. With an increasing load average, blocks get flushed from the cache more often, resulting in more real I/O operations and consequently higher numbers for ru_inblock and ru_outblock. (ru_in + ru_out = BLOCKS R/W) Hope this explains enough. > >Mott Given @ Defense Logistics Agency ,DSAC-TMP, Bldg. 27-1, P.O. Box 1605, ____________________________________________________________________________ Casper H.S. Dik University of Amsterdam | dik@uva.uucp The Netherlands | ...!uunet!mcvax!uva!dik