config: simplify final CPU affinity rule #1261
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Description of execCPUAffinity.final said that if it's not set or empty, the final affinity is the one of container's cgroup. This was done because we thought the kernel changes process' CPU affinity to one of cgroup. It's not the case. To keep the runtime simple, it makes sense to not do anything if the final affinity is not explicitly set. This change does just that. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
kolyshkin
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AkihiroSuda,
crosbymichael,
cyphar,
dqminh,
giuseppe,
hqhq,
mrunalp,
thaJeztah,
tianon and
utam0k
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@kad PTAL |
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I'm fine with new wording. However, in overall, I'd prefer to have that field to be not only for exec, but for all stages of container lifecycle, as we have ideas on how it might be useful in some corner case scenarios even for pid 1 of container... But that's another story :) |
We can rename it to "CPUAffinity" and apply to both exec and init. Feel free to open a PR. |
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Jul 17, 2024
As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
utam0k
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tianon
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kolyshkin
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As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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This is to include - opencontainers/runtime-spec#1261 - opencontainers/runtime-spec#1253 Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Jan 9, 2025
As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Jan 10, 2025
This is to include - opencontainers/runtime-spec#1261 - opencontainers/runtime-spec#1253 Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Jan 15, 2025
As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 Add some tests (alas it's impossible to test initial CPU affinity without adding debug logging to nsexec). Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Jan 16, 2025
As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 CPU affinity can be set in two ways: 1. When creating/starting a container, in config.json's Process.ExecCPUAffinity, which is when applied to all execs. 2. When running an exec, in process.json's CPUAffinity, which applied to a given exec and overrides the value from (1). Add some basic tests. Note that older kernels (RHEL8, Ubuntu 20.04) change CPU affinity of a process to that of a container's cgroup, as soon as it is moved to that cgroup, while newer kernels (Ubuntu 24.04, Fedora 41) don't do that. Because of the above, - it's impossible to really test initial CPU affinity without adding debug logging to libcontainer/nsenter; - for older kernels, there can be a brief moment when exec's affinity is different than either initial or final affinity being set; - exec's final CPU affinity, if not specified, can be different depending on the kernel, therefore we don't test it. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
kolyshkin
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Jan 21, 2025
This is to include - opencontainers/runtime-spec#1261 - opencontainers/runtime-spec#1253 Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
kolyshkin
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Jan 21, 2025
As per - opencontainers/runtime-spec#1253 - opencontainers/runtime-spec#1261 CPU affinity can be set in two ways: 1. When creating/starting a container, in config.json's Process.ExecCPUAffinity, which is when applied to all execs. 2. When running an exec, in process.json's CPUAffinity, which applied to a given exec and overrides the value from (1). Add some basic tests. Note that older kernels (RHEL8, Ubuntu 20.04) change CPU affinity of a process to that of a container's cgroup, as soon as it is moved to that cgroup, while newer kernels (Ubuntu 24.04, Fedora 41) don't do that. Because of the above, - it's impossible to really test initial CPU affinity without adding debug logging to libcontainer/nsenter; - for older kernels, there can be a brief moment when exec's affinity is different than either initial or final affinity being set; - exec's final CPU affinity, if not specified, can be different depending on the kernel, therefore we don't test it. Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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Description of
execCPUAffinity.finalfield (added in #1253) said that if it's not set or empty, the final affinity is the one of container's cgroup. This was done because we thought the kernel changes process' CPU affinity to one of cgroup. It's not always the case (see here).To keep runtimes simple, it makes sense to not do anything if the final affinity is not explicitly set. This change does just that.