We're currently having a problem with the porting from cpu_map from
processes to thread-groups as it happened in 2.7 with commit 5b09341c0
("MEDIUM: cpu-map: replace the process number with the thread group
number"), though it seems that it has deeper roots even in 2.0 and
that it was progressively made worng over time.
The issue stems in the way the per-process and per-thread cpu-sets were
employed over time. Originally only processes were supported. Then
threads were added after an optional "/" and it was documented that
"cpu-map 1" is exactly equivalent to "cpu-map 1/all" (this was clarified
in 2.5 by commit 317804d28 ("DOC: update references to process numbers
in cpu-map and bind-process").
The reality is different: when processes were still supported, setting
"cpu-map 1" would apply the mask to the process itself (and only when
run in the background, which is not documented either and is also a
bug for another fix), and would be combined with any possible per-thread
mask when calculating the threads' affinity, possibly resulting in empty
sets. However, "cpu-map 1/all" would only set the mask for the threads
and not the process. As such the following:
cpu-map 1 odd
cpu-map 1/1-8 even
would leave no CPU while doing:
cpu-map 1/all odd
cpu-map 1/1-8 even
would allow all CPUs.
While such configs are very unlikely to ever be met (which is why this
bug is tagged minor), this is becoming quite more visible while testing
automatic CPU binding during 2.9 development because due to this bug
it's much more common to end up with incorrect bindings.
This patch fixes it by simply removing the .proc entry from cpu_map and
always setting all threads' maps. The process is no longer arbitrarily
bound to the group 1's mask, but in case threads are disabled, we'll
use thread 1's mask since it contains the configured CPUs.
This fix should be backported at least to 2.6, but no need to insist if
it resists as it's easier to break cpu-map than to fix an unlikely issue.
151f9a2808