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.
Since we'll soon want to adjust the "thread-groups" degree of freedom
based on the presence of cpu-map, we first need to be able to detect
if cpu-map was used. This function scans all cpu-map sets to detect if
any is present, and returns true accordingly.
The principle remains the same, but instead of having a single process
and ignoring extra ones, now we set the affinity masks for the respective
threads of all groups.
The doc was updated with a few extra examples.
The man page indicates that CPU_AND() and CPU_ASSIGN() take a variable,
not a const on the source, even though it doesn't make much sense. But
with older libcs, this triggers a build warning:
src/cpuset.c: In function 'ha_cpuset_and':
src/cpuset.c:53: warning: initialization discards qualifiers from pointer target type
src/cpuset.c: In function 'ha_cpuset_assign':
src/cpuset.c:101: warning: initialization discards qualifiers from pointer target type
Better stick stricter to the documented API as this is really harmless
here. There's no need to backport it (unless build issues are reported,
which is quite unlikely).
Fix the macro used to retrieve the max number of cpus on FreeBSD. The
MAXCPU is not properly defined in userspace and always set to 1 despite
the machine architecture. Replace it with CPU_SETSIZE.
See https://freebsd-hackers.freebsd.narkive.com/gw4BeLum/smp-in-machine-params-h#post6
Without this, the following config file is rejected on FreeBSD even if
the machine is SMP :
global
cpu-map 1-2 0-1
This must be backported up to 2.4.
Move cpu_map structure outside of the global struct to a global
variable defined in cpuset.c compilation unit. This allows to reorganize
the includes without having to define _GNU_SOURCE everywhere for the
support of the cpu_set_t.
This fixes the compilation with musl libc, most notably used for the
alpine based docker image.
This fixes the github issue #1235.
No need to backport as this feature is new in the current
2.4-dev.
This module can be used to manipulate a cpu sets in a platform agnostic
way. Use the type cpu_set_t/cpuset_t if available on the platform, or
fallback to unsigned long, which limits de facto the maximum cpu index
to LONGBITS.
