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config-linux: add CFS bandwidth burst #1120

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Jan 23, 2023
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config-linux: add CFS bandwidth burst #1120

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4 changes: 4 additions & 0 deletions config-linux.md
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Expand Up @@ -360,6 +360,9 @@ The following parameters can be specified to set up the controller:

* **`shares`** *(uint64, OPTIONAL)* - specifies a relative share of CPU time available to the tasks in a cgroup
* **`quota`** *(int64, OPTIONAL)* - specifies the total amount of time in microseconds for which all tasks in a cgroup can run during one period (as defined by **`period`** below)
If specified with any (valid) positive value, it MUST be no smaller than `burst` (runtimes MAY generate an error).
* **`burst`** *(uint64, OPTIONAL)* - specifies the maximum amount of accumulated time in microseconds for which all tasks in a cgroup can run additionally for burst during one period (as defined by **`period`** below)
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This feature borrows time now against the future underrun ...

Given this, I don't think "accumulated" is the right choice of word here -- this feature is about borrowing from the future, not accumulating from the past:

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* **`burst`** *(uint64, OPTIONAL)* - specifies the maximum amount of accumulated time in microseconds for which all tasks in a cgroup can run additionally for burst during one period (as defined by **`period`** below)
* **`burst`** *(uint64, OPTIONAL)* - specifies the maximum amount of burst time in microseconds for which all tasks in a cgroup can borrow from future periods during one period (as defined by **`period`** below)

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This feature borrows time now against the future underrun ... is directly from the kernel doc and it's actually accumulating from the past rather than borrowing from future. It intends to say that borrowing time now to prepare for the future underestimation.

If specified, this value MUST be no larger than any positive `quota` (runtimes MAY generate an error).
* **`period`** *(uint64, OPTIONAL)* - specifies a period of time in microseconds for how regularly a cgroup's access to CPU resources should be reallocated (CFS scheduler only)
* **`realtimeRuntime`** *(int64, OPTIONAL)* - specifies a period of time in microseconds for the longest continuous period in which the tasks in a cgroup have access to CPU resources
* **`realtimePeriod`** *(uint64, OPTIONAL)* - same as **`period`** but applies to realtime scheduler only
Expand All @@ -373,6 +376,7 @@ The following parameters can be specified to set up the controller:
"cpu": {
"shares": 1024,
"quota": 1000000,
"burst": 1000000,
"period": 500000,
"realtimeRuntime": 950000,
"realtimePeriod": 1000000,
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3 changes: 3 additions & 0 deletions schema/config-linux.json
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Expand Up @@ -110,6 +110,9 @@
"quota": {
"$ref": "defs.json#/definitions/int64"
},
"burst": {
"$ref": "defs.json#/definitions/uint64"
},
"realtimePeriod": {
"$ref": "defs.json#/definitions/uint64"
},
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1 change: 1 addition & 0 deletions schema/test/config/good/spec-example.json
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Expand Up @@ -275,6 +275,7 @@
"cpu": {
"shares": 1024,
"quota": 1000000,
"burst": 1000000,
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@marquiz marquiz Jan 20, 2023 •
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Period MUST be no smaller than burst -> burst should not be greater than period(?)

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Period MUST be no smaller than burst

Why is this contraint needed? burst can be greater than period.

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You're right. Sorry, my bad, I misread the new content on field description above 🙈

"period": 500000,
"realtimeRuntime": 950000,
"realtimePeriod": 1000000,
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3 changes: 3 additions & 0 deletions specs-go/config.go
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Expand Up @@ -327,6 +327,9 @@ type LinuxCPU struct {
Shares *uint64 `json:"shares,omitempty"`
// CPU hardcap limit (in usecs). Allowed cpu time in a given period.
Quota *int64 `json:"quota,omitempty"`
// CPU hardcap burst limit (in usecs). Allowed accumulated cpu time additionally for burst in a
// given period.
Burst *uint64 `json:"burst,omitempty"`
// CPU period to be used for hardcapping (in usecs).
Period *uint64 `json:"period,omitempty"`
// How much time realtime scheduling may use (in usecs).
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