linux-kernel - [RFC PATCH 1/5] cpumask: Introduce cpu parked mask

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250523181448.3777233-2-sshegde@linux.ibm.com>
Date: Fri, 23 May 2025 23:44:44 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, tglx@...utronix.de, yury.norov@...il.com,
        maddy@...ux.ibm.com
Cc: sshegde@...ux.ibm.com, vschneid@...hat.com, dietmar.eggemann@....com,
        rostedt@...dmis.org, jstultz@...gle.com, kprateek.nayak@....com,
        huschle@...ux.ibm.com, srikar@...ux.ibm.com,
        linux-kernel@...r.kernel.org, linux@...musvillemoes.dk
Subject: [RFC PATCH 1/5] cpumask: Introduce cpu parked mask

CPU is said to be parked, when underlying physical CPU is not 
available. This happens when there is contention for CPU resource in
para-virtualized case. One should avoid using these CPUs. 

Build and maintain this state of parked CPUs. Scheduler will use this
information and push the tasks out as soon as it can. 

Signed-off-by: Shrikanth Hegde <sshegde@...ux.ibm.com>
---
- Not sure if __read_mostly attribute suits for cpu_parked 
since it can change often. Since often means a few mins, it is long time
from scheduler perspective, hence kept it. 

 include/linux/cpumask.h | 14 ++++++++++++++
 kernel/cpu.c            |  3 +++
 2 files changed, 17 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 6a569c7534db..501848303800 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -84,6 +84,7 @@ static __always_inline void set_nr_cpu_ids(unsigned int nr)
  *     cpu_enabled_mask - has bit 'cpu' set iff cpu can be brought online
  *     cpu_online_mask  - has bit 'cpu' set iff cpu available to scheduler
  *     cpu_active_mask  - has bit 'cpu' set iff cpu available to migration
+ *     cpu_parked_mask  - has bit 'cpu' set iff cpu is parked
  *
  *  If !CONFIG_HOTPLUG_CPU, present == possible, and active == online.
  *
@@ -93,6 +94,11 @@ static __always_inline void set_nr_cpu_ids(unsigned int nr)
  *  representing which CPUs are currently plugged in.  And
  *  cpu_online_mask is the dynamic subset of cpu_present_mask,
  *  indicating those CPUs available for scheduling.
+ *
+ *  A CPU is said to be parked when underlying physical CPU(pCPU) is not
+ *  available at the moment. It is recommended not to run any workload on
+ *  that CPU.
+
  *
  *  If HOTPLUG is enabled, then cpu_present_mask varies dynamically,
  *  depending on what ACPI reports as currently plugged in, otherwise
@@ -118,12 +124,14 @@ extern struct cpumask __cpu_enabled_mask;
 extern struct cpumask __cpu_present_mask;
 extern struct cpumask __cpu_active_mask;
 extern struct cpumask __cpu_dying_mask;
+extern struct cpumask __cpu_parked_mask;
 #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
 #define cpu_online_mask   ((const struct cpumask *)&__cpu_online_mask)
 #define cpu_enabled_mask   ((const struct cpumask *)&__cpu_enabled_mask)
 #define cpu_present_mask  ((const struct cpumask *)&__cpu_present_mask)
 #define cpu_active_mask   ((const struct cpumask *)&__cpu_active_mask)
 #define cpu_dying_mask    ((const struct cpumask *)&__cpu_dying_mask)
+#define cpu_parked_mask    ((const struct cpumask *)&__cpu_parked_mask)
 
 extern atomic_t __num_online_cpus;
 
@@ -1146,6 +1154,7 @@ void init_cpu_possible(const struct cpumask *src);
 #define set_cpu_present(cpu, present)	assign_cpu((cpu), &__cpu_present_mask, (present))
 #define set_cpu_active(cpu, active)	assign_cpu((cpu), &__cpu_active_mask, (active))
 #define set_cpu_dying(cpu, dying)	assign_cpu((cpu), &__cpu_dying_mask, (dying))
+#define set_cpu_parked(cpu, parked)    assign_cpu((cpu), &__cpu_parked_mask, (parked))
 
 void set_cpu_online(unsigned int cpu, bool online);
 
@@ -1235,6 +1244,11 @@ static __always_inline bool cpu_dying(unsigned int cpu)
 	return cpumask_test_cpu(cpu, cpu_dying_mask);
 }
 
+static __always_inline bool cpu_parked(unsigned int cpu)
+{
+	return cpumask_test_cpu(cpu, cpu_parked_mask);
+}
+
 #else
 
 #define num_online_cpus()	1U
diff --git a/kernel/cpu.c b/kernel/cpu.c
index a59e009e0be4..532fbfbe3226 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3110,6 +3110,9 @@ EXPORT_SYMBOL(__cpu_dying_mask);
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
+struct cpumask __cpu_parked_mask __read_mostly;
+EXPORT_SYMBOL(__cpu_parked_mask);
+
 void init_cpu_present(const struct cpumask *src)
 {
 	cpumask_copy(&__cpu_present_mask, src);
-- 
2.39.3