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Add units for meter rate to documentation of simple_switch #753

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Apr 25, 2019
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Add units for meter rate to documentation of simple_switch #753

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37a407d
Add units for meter rate
hesingh Apr 11, 2019
84aa5eb
Edited text because meter rate is entered by CLI
hesingh Apr 11, 2019
3bf1a4e
Forgot to change two more lines
hesingh Apr 11, 2019
a906886
Fix burst_size doc and code
hesingh Apr 11, 2019
69c20d3
fix typo
hesingh Apr 11, 2019
cc3f725
Change rate doc
hesingh Apr 11, 2019
96076bc
Revet octets change; update doc
hesingh Apr 11, 2019
a7dbf6e
Fix/add comments, change doc
hesingh Apr 11, 2019
7b4f242
Add context to doc
hesingh Apr 12, 2019
252cbd1
Edited doc; reverted pdchanges, added help to cli;
hesingh Apr 12, 2019
56f8dca
Merge branch 'master' into master
hesingh Apr 12, 2019
0367e3d
Restore pdfixed code
hesingh Apr 16, 2019
048b2ef
Address review comments
hesingh Apr 17, 2019
06967ec
Address review comments
hesingh Apr 19, 2019
8a114ea
Add CLI syntax and test one change to fix rendering on github
hesingh Apr 24, 2019
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Try to fix rendering on github
hesingh Apr 24, 2019
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5 changes: 5 additions & 0 deletions docs/simple_switch.md
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Original file line number Diff line number Diff line change
Expand Up @@ -685,3 +685,8 @@ you have two actions for table `t` where one has the action
`m.read(result_field2)`, or if both of those calls are in the same
action. All calls to the `read()` method for `m` must have the same
result parameter where the result is written.

### BMv2 `meter rate units` implementation notes
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what is this documentation for? The runtime CLI? The Thrift service? The PD API?

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simple_switch_CLI

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that's not accurate then
IIRC, the burst size is in "units" (packets or bytes) and the rate is in "units per microsecond" (https://github.com/p4lang/behavioral-model/blob/master/thrift_src/standard.thrift#L88)

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Wow, even I quoted the same line of code in the Slack channel today. But, seeing the code in pd_helpers.cpp, I saw the conversion from kbps and kbits. This cpp code also happens to be the only code in the behavioral-model repo converting rate and burst_size and thus I assumed the code is used with simpe_switch_CLI as well.

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that's not accurate then
IIRC, the burst size is in "units" (packets or bytes) and the rate is in "units per microsecond" (https://github.com/p4lang/behavioral-model/blob/master/thrift_src/standard.thrift#L88)

There is some confusion. Based on your reply for meter type as packet, its "units in microsecond" and this is the relevant code in pd_helpers.cpp. I see the division by 10^6 for microseconds.

info_rate = static_cast<double>(meter_spec->cir_pps) / 1000000.;

Isn't the user input captured by simple_switch_CLI in meter_spec->cir_pps and thus the user inputs in pps units? Or is the code in pd_helpers.cpp not used at all by simple_switch_CLI?

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The PD layer is not used at all by the CLI. If you look at the CLI code, you will see that it calls the Thrift service directly.
It is fine to have this information in simple_switch.md BTW, but it would be far more useful to improve the runtime_CLI help message for the meter_set_rates CLI command, so that users can get this information directly from the CLI a they are using it.

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Ok, I will edit the simple_switch.md doc for CLI rates and burst_size. Even, I was thinking of adding the help message for the meter_set_rates. I will add that. Thanks!


The user enters the meter rate and burtsize in
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It sounds reasonable that the meter rate is in units of bytes per microsec, but the units of "burst size" should be some kind of unit like bytes. It has nothing to do with time. I do not know if simple_switch uses bytes or some other unit like kilobytes.

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From the names of variables and some of the math done to convert units, it appears like perhaps the burst sizes are specified in multiples of 1000 bits (Kbits would be confusing to many people, I think, as it would often be interpreted as multiples of 1024 bits).

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Also, these are likely the units used when a meter has meter type equal to MeterType.bytes in v1model.

Does BMv2 support different behavior for meters that have a type equal to MeterType.packets ?

If so, what are the units of the meter rates and burst sizes for such meters?

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It sounds reasonable that the meter rate is in units of bytes per microsec, but the units of "burst size" should be some kind of unit like bytes. It has nothing to do with time. I do not know if simple_switch uses bytes or some other unit like kilobytes.

Sorry, I missed the burst_size in bytes. I will change the doc.

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From the names of variables and some of the math done to convert units, it appears like perhaps the burst sizes are specified in multiples of 1000 bits (Kbits would be confusing to many people, I think, as it would often be interpreted as multiples of 1024 bits).

Makes sense to use number of kilo octets.

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Also, these are likely the units used when a meter has meter type equal to MeterType.bytes in v1model.

Does BMv2 support different behavior for meters that have a type equal to MeterType.packets ?

If so, what are the units of the meter rates and burst sizes for such meters?

pps and packets.

units of bytes/microsec.
12 changes: 8 additions & 4 deletions pdfixed/src/pd_helpers.cpp
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Expand Up @@ -34,12 +34,14 @@ pd_bytes_meter_spec_to_rates(p4_pd_bytes_meter_spec_t *meter_spec) {
// bytes per microsecond
info_rate = static_cast<double>(meter_spec->cir_kbps) / 8000.;
burst_size = meter_spec->cburst_kbits * 1000 / 8;
rate.units_per_micros = info_rate; rate.burst_size = burst_size;
rate.units_per_micros = info_rate;
rate.burst_size = burst_size;
rates.push_back(rate);

info_rate = static_cast<double>(meter_spec->pir_kbps) / 8000.;
burst_size = meter_spec->pburst_kbits * 1000 / 8;
rate.units_per_micros = info_rate; rate.burst_size = burst_size;
rate.units_per_micros = info_rate;
rate.burst_size = burst_size;
rates.push_back(rate);

return rates;
Expand All @@ -55,12 +57,14 @@ pd_packets_meter_spec_to_rates(p4_pd_packets_meter_spec_t *meter_spec) {

info_rate = static_cast<double>(meter_spec->cir_pps) / 1000000.;
burst_size = meter_spec->cburst_pkts;
rate.units_per_micros = info_rate; rate.burst_size = burst_size;
rate.units_per_micros = info_rate;
rate.burst_size = burst_size;
rates.push_back(rate);

info_rate = static_cast<double>(meter_spec->pir_pps) / 1000000.;
burst_size = meter_spec->pburst_pkts;
rate.units_per_micros = info_rate; rate.burst_size = burst_size;
rate.units_per_micros = info_rate;
rate.burst_size = burst_size;
rates.push_back(rate);

return rates;
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