# Extremely low buffer usage on perf monitor **URL:** \ **Category:** GNU Radio\ **Created:** [August 6, 2015, 12:33pm UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904 "2015-08-06T12:33:18Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![Rafa\_F](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/958977/32.png) [@Rafa\_F](https://www.ruby-forum.com/u/Rafa_F)\ **Post date:** [August 6, 2015, 12:33pm UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904/1 "2015-08-06T12:33:18Z")
I am looking into CPU and buffer usage of my OOT module via CtrlPort Performance Monitor. I have two flow graphs, a transmitter and a receiver. I can see a quite reasonable performance measures on the receiver side: However, on the transmitter side, buffer usage shows very weird values: It says, the transmitter of my OOT module rarely uses buffer. But, i don’t think so, and actually it uses buffers! At least, I think encoders on the transmitter should use buffers as much as decoders on the receiver does. (Of course, it’s not true that encoder and decoder require same computational cost. But, what I mean is that such tiny value is ridiculous.) I’ve executed the transmitter flow graph several times again and again, that number (1.52…e-5) never changes. My guess is, that number is a floating point representation of 1/(2^16). And 2^16 is 64k. But I have no idea what it means. Can anyone give me a tiny hint of it? Regards Jeon. ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 6, 2015, 2:15pm UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904/2 "2015-08-06T14:15:32Z")
I’m sorry for something that I didn’t write on the previous post. Comparing runtime and buffer, runtime and buffer have different number of blocks. In many cases of mine, buffer shows a fewer blocks than runtime. My guess is that, it’s because buffer of sink blocks don’t have to be monitored. Is what I guess is correct? If so, this might be a problem when I want to monitor a certain block which has an optional output signature so that it is recognized as a sink block. Is there a way to monitor a such block? Regards, Jeon. 2015-08-06 19:31 GMT+09:00 Jeon [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 6, 2015, 9:31pm UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904/3 "2015-08-06T21:31:59Z")
Hi Jeon, only output buffers are counted – because they are the input buffers of the next block “downstream” in your flow graph. Also, a single buffer can only have one block writing to it, but multiple blocks reading from it, so it’s logical to only count the “outputs”; hence, sinks don’t count at all. Would that explain the difference in numbers? Best regards, Marcus ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 7, 2015, 12:20am UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904/4 "2015-08-07T00:20:49Z")
On Thu, Aug 6, 2015 at 8:14 AM, Jeon [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > If so, this might be a problem when I want to monitor a certain block > which has an optional output signature so that it is recognized as a sink > block. > > Is there a way to monitor a such block? > > Regards, > Jeon. If it’s a sink block, then no, it doesn’t have an output buffer and so cannot be monitored this way. If it has an output buffer, it will show up here. > > I’ve executed the transmitter flow graph several times again and again, Those are strange numbers. They should represent a percentage, so all of the numbers in these tables should add up to 1. It’s possible that one buffer is empty during some calls to get the performance counter and we’re not protecting against that, which is causing strange behavior (not exactly a divide-by-zero, but maybe similar?). So no, I don’t quite know. Also, please be careful when sending images in your emails. They make them overly large, and our system might catch and block them instead of letting the pass. Better to either copy the values into a table or post this as a screenshot somewhere and send the link instead. Tom ---
**Author:** ![Jeon](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/e8c25b/32.png) [@Jeon](https://www.ruby-forum.com/u/Jeon)\ **Post date:** [August 7, 2015, 12:43am UTC](https://www.ruby-forum.com/t/extremely-low-buffer-usage-on-perf-monitor/242904/5 "2015-08-07T00:43:36Z")
Just FYI, Jeon’s images are a link (to [imgur.com](http://imgur.com)). Ron