[Ganglia-developers] Linux/cygwin gmond metric poll rate.

[<Ric...@ba...>]

Guys,


the code below is in the cygwin and linux metric.c files.

--------------------------------------------------------
typedef struct {
=20 uint32_t last_read;
=20 uint32_t thresh;
=20 char *name;
=20 char buffer[BUFFSIZE];
} timely_file;

timely_file proc_stat    =3D { 0, 15, "/proc/stat" };
timely_file proc_loadavg =3D { 0, 15, "/proc/loadavg" };
timely_file proc_meminfo =3D { 0, 30, "/proc/meminfo" };
timely_file proc_net_dev =3D { 0, 30, "/proc/net/dev" };

char *update_file(timely_file *tf)
{
=20 int now,rval;
=20 now =3D time(0);
=20 if(now - tf->last_read > tf->thresh) {
=20   rval =3D slurpfile(tf->name, tf->buffer, BUFFSIZE);
=20   if(rval =3D=3D SYNAPSE_FAILURE) {
=20     err_msg("update_file() got an error from slurpfile() reading %s",=

=20             tf->name);
=20     return (char *)SYNAPSE_FAILURE;
=20   }
=20   else tf->last_read =3D now;
=20 }
=20 return tf->buffer;
}
--------------------------------------------------------

In my ganglia setup I have a small number of metrics polled often (5-10
seconds) on a large number
of host (4,000!). I have already observed that values did not seem to
change that fast,
but have only now found the above code. I obviously can't poll fast with
the above code.

Given that metrics are measured only at the rate defined by their poll
time, what is the point
of the above code? Is it to ensure that when (say) cpu_user, cpu_sys,
cpu_wio etc are measured, the
/proc file is only opened once?

Also it seems the delay between /proc file reads is the delay above,
plus the poll delay of the metric.
It this true? I measured this, but did not trace through the code source
to confirm.

So Matt (or a similar guru), can you let me know the intent of this
code?

kind regards,
Richard G
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