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authorNysal Jan K.A <nysal@linux.ibm.com>2024-07-31 05:01:12 +0200
committerMichael Ellerman <mpe@ellerman.id.au>2024-08-13 02:31:24 +0200
commit6c17ea1f3eaa330d445ac14a9428402ce4e3055e (patch)
tree4e5e903107d323ebe0ea0be31f8e1f0fce17f5ad /kernel
parentpowerpc/mm: Fix boot warning with hugepages and CONFIG_DEBUG_VIRTUAL (diff)
downloadlinux-6c17ea1f3eaa330d445ac14a9428402ce4e3055e.tar.xz
linux-6c17ea1f3eaa330d445ac14a9428402ce4e3055e.zip
cpu/SMT: Enable SMT only if a core is online
If a core is offline then enabling SMT should not online CPUs of this core. By enabling SMT, what is intended is either changing the SMT value from "off" to "on" or setting the SMT level (threads per core) from a lower to higher value. On PowerPC the ppc64_cpu utility can be used, among other things, to perform the following functions: ppc64_cpu --cores-on # Get the number of online cores ppc64_cpu --cores-on=X # Put exactly X cores online ppc64_cpu --offline-cores=X[,Y,...] # Put specified cores offline ppc64_cpu --smt={on|off|value} # Enable, disable or change SMT level If the user has decided to offline certain cores, enabling SMT should not online CPUs in those cores. This patch fixes the issue and changes the behaviour as described, by introducing an arch specific function topology_is_core_online(). It is currently implemented only for PowerPC. Fixes: 73c58e7e1412 ("powerpc: Add HOTPLUG_SMT support") Reported-by: Tyrel Datwyler <tyreld@linux.ibm.com> Closes: https://groups.google.com/g/powerpc-utils-devel/c/wrwVzAAnRlI/m/5KJSoqP4BAAJ Signed-off-by: Nysal Jan K.A <nysal@linux.ibm.com> Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com> Reviewed-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20240731030126.956210-2-nysal@linux.ibm.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cpu.c12
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 1209ddaec026..b1fd2a3db91a 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2689,6 +2689,16 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
return ret;
}
+/**
+ * Check if the core a CPU belongs to is online
+ */
+#if !defined(topology_is_core_online)
+static inline bool topology_is_core_online(unsigned int cpu)
+{
+ return true;
+}
+#endif
+
int cpuhp_smt_enable(void)
{
int cpu, ret = 0;
@@ -2699,7 +2709,7 @@ int cpuhp_smt_enable(void)
/* Skip online CPUs and CPUs on offline nodes */
if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
continue;
- if (!cpu_smt_thread_allowed(cpu))
+ if (!cpu_smt_thread_allowed(cpu) || !topology_is_core_online(cpu))
continue;
ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
if (ret)