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PVF validation host: do not alter niceness #4525

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Dec 14, 2021
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@pepyakin pepyakin commented Dec 14, 2021

We wanted to change niceness to accomodate the fact that some of the
preparation tasks are low priority. For example, when a node sees that
there is a new para was onboarded the node may start preparing right
away. Since all other activities are more important, such as network I/O
or validation of the backed candidates and preparation of the
immediatelly needed PVFs.

However, it turned out that this approach does not work: generally
non-root processes can only decrease niceness and they cannot increase
it to the previous value, as was assumed by the code.

Apart from that, #4123
assumes all PVFs are prepared in the same way. Specifically, that if a
PVF preparation failed before, then PVF pre-checking will also report
that it was failed, even though it could happen that preparation failed
due to being low-priority. In order to avoid such cases, we decided to
simplify the whole preparation model. Preparation under low priority
does not work well with that.

Closes #4520

skip check-dependent-cumulus

We wanted to change niceness to accomodate the fact that some of the
preparation tasks are low priority. For example, when a node sees that
there is a new para was onboarded the node may start preparing right
away. Since all other activities are more important, such as network I/O
or validation of the backed candidates and preparation of the
immediatelly needed PVFs.

However, it turned out that this approach does not work: generally
non-root processes can only decrease niceness and they cannot increase
it to the previous value, as was assumed by the code.

Apart from that, #4123
assumes all PVFs are prepared in the same way. Specifically, that if a
PVF preparation failed before, then PVF pre-checking will also report
that it was failed, even though it could happen that preparation failed
due to being low-priority. In order to avoid such cases, we decided to
simplify the whole preparation model. Preparation under low priority
does not work well with that.

Closes #4520
@pepyakin
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Current dependencies on/for this PR:

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@github-actions github-actions bot added the A0-please_review Pull request needs code review. label Dec 14, 2021
@pepyakin pepyakin added B0-silent Changes should not be mentioned in any release notes C1-low PR touches the given topic and has a low impact on builders. D3-trivial 🧸 PR contains trivial changes in a runtime directory that do not require an audit. labels Dec 14, 2021
@pepyakin pepyakin merged commit 69b4791 into master Dec 14, 2021
@pepyakin pepyakin deleted the pep-pvf-not-nice branch December 14, 2021 16:17
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A0-please_review Pull request needs code review. B0-silent Changes should not be mentioned in any release notes C1-low PR touches the given topic and has a low impact on builders. D3-trivial 🧸 PR contains trivial changes in a runtime directory that do not require an audit.
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PVF validation host: Remove nice changing code
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