The patch titled
Subject: sched/isolation: add cpu_is_isolated() API
has been added to the -mm mm-unstable branch. Its filename is
sched-isolation-add-cpu_is_isolated-api.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/sched-isolation-add-cpu_is_isolated-api.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
Subject: sched/isolation: add cpu_is_isolated() API
Date: Fri, 17 Mar 2023 14:44:47 +0100
Patch series "memcg, cpuisol: do not interfere pcp cache charges draining
with cpuisol workloads".
Leonardo has reported [1] that pcp memcg charge draining can interfere
with cpu isolated workloads. The said draining is done from a WQ context
with a pcp worker scheduled on each CPU which holds any cached charges for
a specific memcg hierarchy. Operation is not really a common operation
[2]. It can be triggered from the userspace though so some care is
definitely due.
Leonardo has tried to address the issue by allowing remote charge draining
[3]. This approach requires an additional locking to synchronize pcp
caches sync from a remote cpu from local pcp consumers. Even though the
proposed lock was per-cpu there is still potential for contention and less
predictable behavior.
This patchset addresses the issue from a different angle. Rather than
dealing with a potential synchronization, cpus which are isolated are
simply never scheduled to be drained. This means that a small amount of
charges could be laying around and waiting for a later use or they are
flushed when a different memcg is charged from the same cpu. More details
are in patch 2. The first patch from Frederic is implementing an
abstraction to tell whether a specific cpu has been isolated and therefore
require a special treatment.
This patch (of 2):
Provide this new API to check if a CPU has been isolated either through
isolcpus= or nohz_full= kernel parameter.
It aims at avoiding kernel load deemed to be safely spared on CPUs running
sensitive workload that can't bear any disturbance, such as pcp cache
draining.
Link: https://lkml.kernel.org/r/20230317134448.11082-1-mhocko@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20230317134448.11082-2-mhocko@xxxxxxxxxx
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Roman Gushchin <roman.gushchin@xxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Leonardo Bras <leobras@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/include/linux/sched/isolation.h~sched-isolation-add-cpu_is_isolated-api
+++ a/include/linux/sched/isolation.h
@@ -46,6 +46,12 @@ static inline bool housekeeping_enabled(
static inline void housekeeping_affine(struct task_struct *t,
enum hk_type type) { }
+
+static inline bool housekeeping_test_cpu(int cpu, enum hk_type type)
+{
+ return true;
+}
+
static inline void housekeeping_init(void) { }
#endif /* CONFIG_CPU_ISOLATION */
@@ -58,4 +64,10 @@ static inline bool housekeeping_cpu(int
return true;
}
+static inline bool cpu_is_isolated(int cpu)
+{
+ return !housekeeping_test_cpu(cpu, HK_TYPE_DOMAIN) ||
+ !housekeeping_test_cpu(cpu, HK_TYPE_TICK);
+}
+
#endif /* _LINUX_SCHED_ISOLATION_H */
_
Patches currently in -mm which might be from frederic@xxxxxxxxxx are
sched-isolation-add-cpu_is_isolated-api.patch
