# Sheduler: do not consume all "input items" and return 0 "output items" **URL:** \ **Category:** GNU Radio\ **Created:** [April 3, 2014, 6:11pm UTC](https://www.ruby-forum.com/t/sheduler-do-not-consume-all-input-items-and-return-0-output-items/240242 "2014-04-03T18:11:40Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [April 3, 2014, 6:11pm UTC](https://www.ruby-forum.com/t/sheduler-do-not-consume-all-input-items-and-return-0-output-items/240242/1 "2014-04-03T18:11:40Z")
* * * Discuss-gnuradio mailing list removed\_email\_address@domain.invalid [https://lists.gnu.org/mailman/listinfo/discuss-gnuradio](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) ---
**Author:** ![squeegy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dec6dc/32.png) [@squeegy](https://www.ruby-forum.com/u/squeegy)\ **Post date:** [April 4, 2014, 12:11am UTC](https://www.ruby-forum.com/t/sheduler-do-not-consume-all-input-items-and-return-0-output-items/240242/2 "2014-04-04T00:11:25Z")
On Thu, Apr 3, 2014 at 12:10 PM, Alex W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 1. Does it deteroarate the performance of my flowgraph when I do not > consume and return as much items as possible? (The fixed numbers are 500 to > 1000). If yes, how much? Hi Alex, Yes, this will negatively affect the performance of your application. Every time you return from work, the scheduler has to set everything up again for the next entry to work, which means more overhead. How much this affects you is determined by a number of factors and we (right now) don’t have the ability to compute it. Instead, we have the Performance Counters and Performance Monitor system in place to allow you to see how your blocks are behaving. It might not be affecting you too badly in the end, depending on what you’re doing and what you need to be doing. For something like this, you might have to think to yourself what’s the tradeoff in efficiency between the block and your time in writing the block to make the most use of the number of items you’ve received. If the block’s performance is a bottleneck for your system, this is definitely something to look in to. > Alex Again, yes, because you’re causing the scheduler to go through a lot of extra work. This might help you out: > **[Explaining the GNU Radio Scheduler — Rondeau Research](http://www.trondeau.com/blog/2013/9/15/explaining-the-gnu-radio-scheduler.html)** > > The most important and distinguishing piece of GNU Radio is the underlying scheduler and framework for implementing and connecting the signal processing blocks. While there are many other libraries of DSP blocks available, it's GNU Radio's scheduler... Also, for something like this, you can use forecast to tell the scheduler how many input items you require given a set of output items. Or, maybe more helpfully for something like this, you can receive a vector of items that’s the size of the correlation you are performing, so one item is actually N samples for the correlation. Your IO signature would be something like gr::io\_signature(1, 1, corr\_size\*sizeof(gr\_complex)). Tom ---
**Author:** ![squeegy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dec6dc/32.png) [@squeegy](https://www.ruby-forum.com/u/squeegy)\ **Post date:** [April 4, 2014, 3:12am UTC](https://www.ruby-forum.com/t/sheduler-do-not-consume-all-input-items-and-return-0-output-items/240242/3 "2014-04-04T03:12:29Z")
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**Author:** ![squeegy](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/s/dec6dc/32.png) [@squeegy](https://www.ruby-forum.com/u/squeegy)\ **Post date:** [April 7, 2014, 8:39pm UTC](https://www.ruby-forum.com/t/sheduler-do-not-consume-all-input-items-and-return-0-output-items/240242/4 "2014-04-07T20:39:32Z")
On Thu, Apr 3, 2014 at 9:11 PM, Alex W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > Why am I getting worse performance with those few passed elements? > > Alex Hard to say, but that’s one thing that our new Performance Monitor tool is supposed to help you find out. The big thing in these cases is the scheduler. You might be calling into things far more often than you both want and expect, causing overhead in the scheduler to set up the blocks. If you’re looking at performance issues, looking into your interaction with the scheduler is key. Tom