[06/10] cpu/SMT: Create topology_smt_thread_allowed()
Commit Message
From: Michael Ellerman <mpe@ellerman.id.au>
A subsequent patch will enable partial SMT states, ie. when not all SMT
threads are brought online.
To support that, add an arch helper which checks whether a given CPU is
allowed to be brought online depending on how many SMT threads are
currently enabled.
Call the helper from cpu_smt_enable(), and cpu_smt_allowed() when SMT is
enabled, to check if the particular thread should be onlined. Notably,
also call it from cpu_smt_disable() if CPU_SMT_ENABLED, to allow
offlining some threads to move from a higher to lower number of threads
online.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
arch/x86/include/asm/topology.h | 2 ++
arch/x86/kernel/smpboot.c | 15 +++++++++++++++
kernel/cpu.c | 10 +++++++++-
3 files changed, 26 insertions(+), 1 deletion(-)
@@ -144,6 +144,7 @@ int topology_phys_to_logical_pkg(unsigned int pkg);
int topology_phys_to_logical_die(unsigned int die, unsigned int cpu);
bool topology_is_primary_thread(unsigned int cpu);
bool topology_smt_threads_supported(unsigned int threads);
+bool topology_smt_thread_allowed(unsigned int cpu);
#else
#define topology_max_packages() (1)
static inline int
@@ -157,6 +158,7 @@ static inline int topology_max_die_per_package(void) { return 1; }
static inline int topology_max_smt_threads(void) { return 1; }
static inline bool topology_is_primary_thread(unsigned int cpu) { return true; }
static inline bool topology_smt_threads_supported(unsigned int threads) { return false; }
+static inline bool topology_smt_thread_allowed(unsigned int cpu) { return false; }
#endif
static inline void arch_fix_phys_package_id(int num, u32 slot)
@@ -290,6 +290,21 @@ bool topology_smt_threads_supported(unsigned int threads)
return threads == 1 || threads == smp_num_siblings;
}
+/**
+ * topology_smt_thread_allowed - When enabling SMT check whether this particular
+ * CPU thread is allowed to be brought online.
+ * @cpu: CPU to check
+ */
+bool topology_smt_thread_allowed(unsigned int cpu)
+{
+ /*
+ * No extra logic s required here to support different thread values
+ * because threads will always == 1 or smp_num_siblings because of
+ * topology_smt_threads_supported().
+ */
+ return true;
+}
+
/**
* topology_phys_to_logical_pkg - Map a physical package id to a logical
*
@@ -468,7 +468,7 @@ early_param("nosmt", smt_cmdline_disable);
static inline bool cpu_smt_allowed(unsigned int cpu)
{
- if (cpu_smt_control == CPU_SMT_ENABLED)
+ if (cpu_smt_control == CPU_SMT_ENABLED && topology_smt_thread_allowed(cpu))
return true;
if (topology_is_primary_thread(cpu))
@@ -2283,6 +2283,12 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
for_each_online_cpu(cpu) {
if (topology_is_primary_thread(cpu))
continue;
+ /*
+ * Disable can be called with CPU_SMT_ENABLED when changing
+ * from a higher to lower number of SMT threads per core.
+ */
+ if (ctrlval == CPU_SMT_ENABLED && topology_smt_thread_allowed(cpu))
+ continue;
ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE);
if (ret)
break;
@@ -2317,6 +2323,8 @@ 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 (!topology_smt_thread_allowed(cpu))
+ continue;
ret = _cpu_up(cpu, 0, CPUHP_ONLINE);
if (ret)
break;