Re: getrusage vs /proc/pid/stat?

[Pete Wyckoff <pw@osc.edu>]

dank@kegel.com said:
> I'd like to monitor CPU, memory, and I/O utilization in a 
> long-running multithreaded daemon under kernels 2.2, 2.4,
> and possibly also Solaris (#ifdefs are ok).
> 
> getrusage() looked promising, and might even work for CPU utilization.
> Dunno if it returns info for all child threads yet, haven't tried it.
> In Linux, though, getrusage() doesn't return any info about RAM.
> 
> I know I can get the RSS and VSIZE under Linux by parsing /proc/pid/stat,
> but was hoping for a faster interface (although I suppose a seek,
> a read, and an ascii parse isn't *that* slow).  Is /proc/pid/stat
> the only way to go under Linux to monitor RSS?

getrusage() isn't really the system call you want for this.

There is a max RSS value, which linux could support but doesn't, but
you seem to want to see the current RSS over time.  Search the archive
for various patches/complaints about getrusage.

For vsize, most OSes offer time-integral averages of text, data, and
stack sizes via getrusage().  Again, more of an aggregate than a current
snapshot, and again, linux returns zero for these currently.

		-- Pete