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Top Forums Programming How can I get a processor's CPU Percentage? Post 8672 by Perderabo on Tuesday 16th of October 2001 11:24:11 AM
Old 10-16-2001
Kernels always have some code built in to gather statistics. In the case of cpus, several times a second a clock routine fires off and increments one element of a structure. The structure will have counters for idle, user, system, and so on.

In the old days, you could get the structure if you knew its name. You would run nlist(3) on the kernel's symbol table to get the address of the structure. Then you opened /dev/kmem. did a seek to the address and read the structure. The c definations of the structures were usually in /usr/include. This still can be made to work on hp-ux, but the required information is no longer supplied in /usr/include. Skilled gurus can reverse-engineer it, but it's difficult. Vic Able has done this to get lsof to work on recent versions of HP-UX, a feat that very few could match.

New system calls like pstat are the way of the future. And pstat works well enough. Why do you want an alternative?
 

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nlist(3UCB)					     SunOS/BSD Compatibility Library Functions					       nlist(3UCB)

NAME
nlist - get entries from symbol table SYNOPSIS
/usr/ucb/cc [ flag ... ] file ... #include <nlist.h> int nlist(filename, nl); char *filename; struct nlist *nl; DESCRIPTION
nlist() examines the symbol table from the executable image whose name is pointed to by filename, and selectively extracts a list of values and puts them in the array of nlist structures pointed to by nl. The name list pointed to by nl consists of an array of structures contain- ing names, types and values. The n_name field of each such structure is taken to be a pointer to a character string representing a symbol name. The list is terminated by an entry with a NULL pointer (or a pointer to a NULL string) in the n_name field. For each entry in nl, if the named symbol is present in the executable image's symbol table, its value and type are placed in the n_value and n_type fields. If a symbol cannot be located, the corresponding n_type field of nl is set to zero. RETURN VALUES
Upon normal completion, nlist() returns the number of symbols that were not located in the symbol table. If an error occurs, nlist() returns -1 and sets all of the n_type fields in members of the array pointed to by nl to zero. SEE ALSO
nlist(3ELF), a.out(4) NOTES
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system libraries or in multi-thread applications is unsupported. Only the n_value field is compatibly set. Other fields in the nlist structure are filled with the ELF (Executable and Linking Format) values (see nlist(3ELF) and a.out(4)). SunOS 5.10 3 May 1994 nlist(3UCB)
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