avg_latency Measure

[ Edited ]

Do anyone knows what this numbers means?



















How can I read the avg_latency counter? Which measure and unit is used in it?

Re: avg_latency Measure

For a general overview of how the performance counter system works, read through the description found in the SDK here:

<sdk dir>/doc/ontapi/ontapi_1.11/perf/index.html

Of specific interest is the explanation of how to interpret the various counter types:

  • raw: single counter value is used
  • delta: change in counter value between two samples is used
  • rate: delta divided by the time in seconds between samples is used
  • average: delta divided by the delta of a base counter is used
  • percent: 100*average is used

To understand more about a specific counter you can get details from the perf-object-counter-list-info API call:

        <desc>Average latency in microseconds for all operations on the volume</desc>

Armed with this info, you should be able to interpret and present the latency values you are interested in. Make two calls to perf-object-get-instances, with a delay between them. Include both avg_latency and total_ops ( the base counter ).

From above we know 'average: delta divided by the delta of a base counter is used'. So perform the following calculation:

(avg_latency2-avg_latency1) / (total_ops2-total_ops1)   => average latency in microseconds

To sanity test your application, compare your output with the output from ONTAP via the CLI:

Actual numbers: (598624907-596952932) / (149998706-149866390) => 12.636

filer1> stats show volume:vol0:avg_latency


Additionally, I'm not sure what language you are working with, but within the samples directory of the SDK there are a couple of perf related applications.


Re: avg_latency Measure

Hi Ryan,

Your post has helped me immensely. A thousand thankyous.


rle Former NetApp Employee

Re: avg_latency Measure

You might want to check out this post for some Perl examples using the perf APIs.


   - Rick -

Re: avg_latency Measure

Once again - very helpful. Thankyou.