Related git commits, starting with the first related change, and finishing with
the fix required.
The intermediary commits provide some context used later to understand the
required dependencies.
---
The initial commit changed __get_nprocs() to use sched_getaffinity()
instead of sysfs and procfs.
It now returns the number of processors that the process can run on, which can
be restricted with
CPU affinity masks (i.e., sched_setaffinity()). Previously, it returned the
number of processors
available in the system (without any restriction due to CPU affinity masks).
commit 903bc7dcc2acafc40be11639767e10a2de712649
Author: Adhemerval Zanella <[email protected]>
Date: Thu Mar 25 09:30:07 2021 -0300
linux: Use sched_getaffinity for __get_nprocs (BZ #27645)
<...> The initial scratch buffer <...>
But it used a buffer approach that turned out to be problematic, and was fixed
in:
commit eb68d7d23cc411acdf68a60f194343a6774d6194
Author: Florian Weimer <[email protected]>
Date: Wed Jun 30 17:41:38 2021 +0200
Linux: Avoid calling malloc indirectly from __get_nprocs
<...>
scratch buffers in __get_nprocs may result in infinite recursion.
Now, this commit is what changed malloc() to "formally" use that
implementation.
Note: that implementation was already being used, as the code used
__get_nprocs()
which was already using sched_getaffinity() per the first commit above (and also
implied by the infinite recursion in the second commit above).
commit 11a02b035b464ab6813676adfd19c4a59c36d907
Author: Adhemerval Zanella <[email protected]>
Date: Mon Sep 6 12:22:54 2021 -0300
misc: Add __get_nprocs_sched
This is an internal function meant to return the number of avaliable
processor where the process can scheduled, different than the
__get_nprocs which returns a the system available online CPU.
The Linux implementation currently only calls __get_nprocs(), which
in tuns calls sched_getaffinity.
<...>
@@ -878,7 +878,7 @@ arena_get2 (size_t size, mstate avoid_arena)
<...>
- int n = __get_nprocs ();
+ int n = __get_nprocs_sched ();
The shortly-following commit _reverted_ the original behavior to __get_nprocs(),
(back to sysfs and procs) and _moved_ the new behavior for __get_nprocs_sched()
(based on sched_getaffinity()).
commit 342298278eabc75baabcaced110a11a02c3d3580
Author: Adhemerval Zanella <[email protected]>
Date: Mon Sep 6 14:19:51 2021 -0300
linux: Revert the use of sched_getaffinity on get_nproc [sic:
__get_nprocs] (BZ #28310)
<...>
The main issue using sched_getaffinity changed the symbols semantic
from system-wide scope of online CPUs to per-process one (which can
be changed with kernel cpusets or book [sic: boot] parameters in
VM).
This patch reverts mostly of the 903bc7dcc2acafc40, with the
<...>
-__get_nprocs (void)
+__get_nprocs_sched (void)
<...>
int r = INTERNAL_SYSCALL_CALL (sched_getaffinity, 0, cpu_bits_size,
cpu_bits);
<...>
-__get_nprocs_sched (void)
+__get_nprocs (void)
<...>
+ int fd = __open_nocancel ("/sys/devices/system/cpu/online", flags);
<...>
+ fd = __open_nocancel ("/proc/stat", flags);
<...>
However, it did _not_ revert the change in arena_get2(), which was done
in:
commit 472894d2cfee5751b44c0aaa71ed87df81c8e62e
Author: Adhemerval Zanella <[email protected]>
Date: Wed Oct 11 13:43:56 2023 -0300
malloc: Use __get_nprocs on arena_get2 (BZ 30945)
This restore the 2.33 semantic for arena_get2. It was changed by
11a02b035b46 to avoid arena_get2 call malloc (back when __get_nproc
was refactored to use an scratch_buffer - 903bc7dcc2acafc). The
__get_nproc was refactored over then and now it also avoid to call
malloc.
--
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https://bugs.launchpad.net/bugs/2089789
Title:
malloc performance degradation with CPU affinity masks
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