View source for Comparing Canister Cycles vs Performance Counter

The example walks through a scenario of charging cycles that includes inter-canister calls and how the performance counter relates to the work done by canisters.

== Setup ==
# The ''User'' sends an 1KiB ''Ingress Message'' to ''Canister A''
# The ''Canister A'' calls ''Canister B'' with an 2KiB ''Update Call''
# The ''Canister B'' responds to ''Canister A'' with an 300-byte reply
# The ''Canister A'' responds to ''User'' with an 500-byte reply

== Example Cycles Flow ==

'''Naming conventions:'''

* <code>1K == 1'000</code>
* <code>1KiB == 1'024 bytes</code>
* <code>1M == 1'000'000</code>
* <code>1MiB == 1'048'576 bytes</code>
* <code>1B == 1'000'000'000</code>
* <code>1T == 1'000'000'000'000</code>

{| class="wikitable" style="text-align:right"
|-
!style=text-align:left| Example Step !! Canister A<br>Cycles Balance !! Canister A<br>Perf Counter !! Canister B<br>Cycles Balance !! Canister B<br>Perf Counter
|-
|style=text-align:left| 1. Initial state || <code>1T</code> || <code>N/A</code><sup>1)</sup> || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 2. ''Canister A'' receives 1KiB ''Ingress Message'' || -1,2M<br>-1KiB*2K<br><code>≈999'996M</code> || <code>N/A</code><sup>1)</sup> || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 3. ''Canister A'' starts execution <sup>2)</sup> || -590K<br>-5B/10*4<br><code>≈997'996M</code> || <code>0</code><br>(5B limit) || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 4. ''Canister A'' executes 100M WASM instructions || <code>997'996M</code> || +100M<br><code>=100M</code><br>(5B limit) || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 5. ''Canister A'' sends 2KiB call to ''Canister B'' <sup>3)</sup> || -260K<br>-2KiB*1K<br>-2MiB*1K<br>-590K<br>-5B/10*4<br><code>≈993'897M</code> || +3*21<br>+2KiB<br><code>≈100M</code><br>(5B limit) || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 6. ''Canister A'' finishes execution <sup>4)</sup> || +(5B-100M)*4/10<br><code>≈995'857M</code> || <code>N/A</code><sup>1)</sup> || <code>1T</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 7. ''Canister B'' starts execution <sup>2)</sup>|| <code>995'857M</code> || <code>N/A</code><sup>1)</sup> || -590K<br>-5B/10*4<br><code>≈997'999M</code> || <code>0</code><br>(5B limit)
|-
|style=text-align:left| 8. ''Canister B'' executes 100M WASM instructions || <code>995'857M</code> || <code>N/A</code><sup>1)</sup> || <code>997'999M</code> || +100M<br><code>=100M</code><br>(5B limit)
|-
|style=text-align:left| 9. ''Canister B'' sends 300-byte reply to ''Canister A'' || <code>995'857M</code> || <code>N/A</code><sup>1)</sup> || <code>997'999M</code> || +2*21<br>+300<br><code>≈100M</code><br>(5B limit)
|-
|style=text-align:left| 10. ''Canister B'' finishes execution <sup>4)</sup> || <code>995'857M</code> || <code>N/A</code><sup>1)</sup> || +(5B-100M)*4/10<br><code>≈999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 11. ''Canister A'' receives a reply from ''Canister B'' <sup>5)</sup> || +(2MiB-300)*1K<br><code>≈997'953M</code> || <code>N/A</code><sup>1)</sup> || <code>999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 12. ''Canister A'' starts reply callback execution <sup>6)</sup> || <code>997'953M</code> || <code>0</code><br>(5B limit)  || <code>999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 13. ''Canister A'' executes 100M WASM instructions || <code>997'953M</code> || +100M<br><code>=100M</code><br>(5B limit) || <code>999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 14. ''Canister A'' sends 500-byte reply to ''User'' || <code>997'953M</code> || +2*21<br>+500<br><code>≈100M</code><br>(5B limit) || <code>999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
|style=text-align:left| 15. ''Canister A'' finishes execution <sup>4)</sup> || +(5B-100M)*4/10<br><code>≈999'913M</code> || <code>N/A</code><sup>1)</sup> || <code>999'959M</code> || <code>N/A</code><sup>1)</sup>
|-
!style=text-align:left| Total: !! <code>~87M Cycles</code><br>for ~200M WASM Instructions Executed<br>+ messaging !!  !! <code>~41M Cycles</code><br>for ~100M WASM Instructions Executed<br>+ messaging !!
|}


'''Notes:'''
# The ''Performance Counter'' is available only during execution, so it's marked as <code>N/A</code> when the execution has not started yet.
# The Canister get charged:
#; 590K : for the update message execution
#; 5B/10*4 : for 5B instructions it can potentially execute
# The Canister get charged:
#; 260K : for the inter-canister call
#; 2KiB * 1'000 : for byte transmission
#; 2MiB * 1K : for the maximum reply size
#; 590K : for the reply update message execution
#; 5B/10*4 : for 5B instructions limit it can potentially execute in the reply handler
# The Canister gets a refund for the unused Instructions.
# The Canister gets a refund for the unused reply bytes.
# The Canister has already been charged in step 5 for the reply execution and 5B instructions.

== References ==
# [https://smartcontracts.org/docs/current/references/ic-interface-spec The Internet Computer Interface Specification]
# [https://smartcontracts.org/docs/current/developer-docs/updates/computation-and-storage-costs The Internet Computer Computation and Storage Costs]
# [https://www.youtube.com/watch?v=YL4R4jQ78u0 Community Conversations | Charging Canister Cycles]