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config-linux: clarify the handling of ClosID RDT parameter #1104

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config-linux: clarify the handling of ClosID RDT parameter #1104

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config-linux: fix indentation on IntelRdt
marquiz Apr 26, 2021
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config-linux: clarify the handling of ClosID RDT parameter
marquiz Apr 26, 2021
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16 changes: 9 additions & 7 deletions config-linux.md
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Expand Up @@ -535,19 +535,21 @@ The following parameters can be specified for the container:
* **`l3CacheSchema`** *(string, OPTIONAL)* - specifies the schema for L3 cache id and capacity bitmask (CBM).
The value SHOULD start with `L3:` and SHOULD NOT contain newlines.
* **`memBwSchema`** *(string, OPTIONAL)* - specifies the schema of memory bandwidth per L3 cache id.
* The value MUST start with `MB:` and MUST NOT contain newlines.
The value MUST start with `MB:` and MUST NOT contain newlines.

* If both `l3CacheSchema` and `memBwSchema` are set, runtimes MUST write the combined value to the `schemata` file in that sub-directory discussed in `closID`.
The following rules on parameters MUST be applied:

* If `l3CacheSchema` contains a line beginning with `MB:`, the value written to `schemata` file MUST be the non-`MB:` line(s) from `l3CacheSchema` and the line from `memBWSchema`.
* If both `l3CacheSchema` and `memBwSchema` are set, runtimes MUST write the combined value to the `schemata` file in that sub-directory discussed in `closID`.

* If either `l3CacheSchema` or `memBwSchema` is set, runtimes MUST write the value to the `schemata` file in the that sub-directory discussed in `closID`.
* If `l3CacheSchema` contains a line beginning with `MB:`, the value written to `schemata` file MUST be the non-`MB:` line(s) from `l3CacheSchema` and the line from `memBWSchema`.
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@marquiz I am looking at the specs to implement this in crun but I don't understand this rule.

Can you give an example? Should it be dropped (at least I don't see any special handling in runc either for this)?

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@giuseppe the idea is that if you have

l3CacheSchema: "L3:foobar\nMB:abcd"
memBWSchema: "MB:xyzy"

Then you'd actually write L3:foobar\nMB:xyzy to the schemata file.

I don't think this has been implemented anywhere. I didn't write this particular formulation, and TBH, I wouldn't probably bother implementing it. I think the fields and there handling is just ambiguously specified, e.g. somehow it's implied that l3CacheSchema could contain multiple lines but memBWSchema only one line. What if l3CacheSchema contains L3:... but memBWSchema: contains L3:... (and other similar questions)...

I try to address the problems in #1230

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thanks, I understand now. Still feels weird to specify that MB: is filtered out instead of just not expecting such a case :-) but I guess we can live with it at this point


* If neither `l3CacheSchema` nor `memBwSchema` is set, runtimes MUST NOT write to `schemata` files in any `resctrl` pseudo-filesystems.
* If either `l3CacheSchema` or `memBwSchema` is set, runtimes MUST write the value to the `schemata` file in the that sub-directory discussed in `closID`.

* If `closID` is set, `l3CacheSchema` and/or `memBwSchema` is set, runtimes MUST compare `l3CacheSchema` and/or `memBwSchema` value with `schemata` file, and [generate an error](runtime.md#errors) if doesn't match.
* If neither `l3CacheSchema` nor `memBwSchema` is set, runtimes MUST NOT write to `schemata` files in any `resctrl` pseudo-filesystems.

* If `closID` is set, and neither of `l3CacheSchema` and `memBwSchema` are set, runtime MUST check if corresponding pre-configured directory `closID` is present in mounted `resctrl`. If such pre-configured directory `closID` exists, runtime MUST assign container to this `closID` and [generate an error](runtime.md#errors) if directory does not exist.
* If `closID` is set, `l3CacheSchema` and/or `memBwSchema` is set, runtimes MUST compare `l3CacheSchema` and/or `memBwSchema` value with `schemata` file, and [generate an error](runtime.md#errors) if doesn't match.

* If `closID` is set, and neither of `l3CacheSchema` and `memBwSchema` are set, runtime MUST check if corresponding pre-configured directory `closID` is present in mounted `resctrl`. If such pre-configured directory `closID` exists, runtime MUST assign container to this `closID` and [generate an error](runtime.md#errors) if directory does not exist.

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Ah, you do this in the second commit. Nice!



### Example
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