On 06/09/2016 08:24 PM, Nathan Scott wrote:
> Hi Will,
>
> ----- Original Message -----
>> [...] How, are the PCP metrics checked
>> to see if they are accurate/reasonable?
>
> It depends - various strategies exist depending on the PMDA and the nature of
> the values being extracted, and the mechanisms involves. There's some
> examples
> over in qa/{778,835,876,987,1113} ... just a small subset to give a taste.
>
>> For estimating network utilization using PCP the network.interface.baudrate
>> and network.interface.speed metrics should provide some indication of the
>> interface speed. However, looking at the numbers produced by pmval below
>> they don't seem to be reasonable for 1Gbps ethernet connection of em1.
>
> There's a couple of ways interface speed is extracted - ioctl and sysfs;
> depends
> on kernel version. The code is over in src/pmdas/linux/proc_net_dev.c - see
> the
> REFRESH_NET_SPEED references there. The code is dependent on the
> kernel/drivers
> giving good values - and there's also issues like pcp commit 9b616ace2284b622
> to
> factor in from out of left field.
>
> That said there could certainly be a PCP bug or two lurking here also. Best
> way
> to step through exactly what's happening here is:
>
> $ gdb --args /usr/bin/pminfo -L -K clear -K
> add,60,`pwd`/src/pmdas/linux/pmda_linux network.interface.speed
>
> ... then set breakpoints in places like refresh_net_dev_ioctl, then "r" in
> gdb.
>
> cheers.
>
> --
> Nathan
>
Hi Nathan,
Thanks for the pointers to existing tests. I am glad to hear that there are
some sanity checks in the pcp qa testsuite. I understand that not every metric
can be sanity checked, but having a larger set of them be correct will make it
less likely for people to be mislead by bogus values.
I will take a closer look at why I am getting the odd values for
network.interface.speed and network.interface.baudrate.
-Will
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