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Old 10-19-2006, 12:23 PM
"William W. Austin"
Default kernel/accounting question ...

(I know that this question might be more reasonable on a kernel list,
but a while back I posted the question twice and got no answers.)

The acct struct is defined in /usr/include/sys/acct.h includes both
ac_io and ac_rw for bytes transferred and blocks read or written,
respectively. Fair and good - works (on paper) similarly to unix,
solaris, hp-ux, etc.

However, in the kernel code [kernel/acct.c], ac_io (char) and ac_rw
(blocks) are always set to 0 by these two lines:

ac.ac_io = encode_comp_t(0 /* current->io_usage */);
ac.ac_rw = encode_comp_t(ac.ac_io / 1024);

For most purposes, this probably wouldn't be an issue, but I also do
extensive performance analysis on several platforms and have written a
fairly compresive accounting package (as a wraparound for psacct or as
a standalone) including both an improved acctcom and a built-in
reporter for it.

Does anyone know wby the kernel zero's out the bytes transferred data?
(Overhead comes to mind.) Not that it makes a huge differnce for my
purposes (I had to write some wraparound code to make a
"best-guestimate" about the data I'm missing), but curiosity is bugging
me now. When I compile my program on other OS's I get useful data for
char and block i/o and I'd like to find out whether there is something
obvious that I'm just totally missing here...).


william w. austin waustin@speakeasy.net
"life is just another phase i'm going through. this time, anyway ..."

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