[PATCH v11 2/4] arch_topology: Support SMT control for OF based system

Yicong Yang
2025-02-18T14:17:57Z

From: Yicong Yang <yangyicong@hisilicon.com>

On building the topology from the devicetree, we've already
gotten the SMT thread number of each core. Update the largest
SMT thread number and enable the SMT control by the end of
topology parsing.

The core's SMT control provides two interface to the users [1]:
1) enable/disable SMT by writing on/off
2) enable/disable SMT by writing thread number 1/max_thread_number

If a system have more than one SMT thread number the 2) may
not handle it well, since there're multiple thread numbers in the
system and 2) only accept 1/max_thread_number. So issue a warning
to notify the users if such system detected.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-devices-system-cpu#n542

Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
---
drivers/base/arch_topology.c | 27 +++++++++++++++++++++++++++
1 file changed, 27 insertions(+)

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 3ebe77566788..23f425a9d77a 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -11,6 +11,7 @@
#include <linux/cleanup.h>
#include <linux/cpu.h>
#include <linux/cpufreq.h>
+#include <linux/cpu_smt.h>
#include <linux/device.h>
#include <linux/of.h>
#include <linux/slab.h>
@@ -506,6 +507,10 @@ core_initcall(free_raw_capacity);
#endif

#if defined(CONFIG_ARM64) || defined(CONFIG_RISCV)
+
+/* Maximum SMT thread number detected used to enable the SMT control */
+static unsigned int max_smt_thread_num;
+
/*
* This function returns the logic cpu number of the node.
* There are basically three kinds of return values:
@@ -565,6 +570,16 @@ static int __init parse_core(struct device_node *core, int package_id,
i++;
} while (1);

+ /*
+ * If max_smt_thread_num has been initialized and doesn't match
+ * the thread number of this entry, then the system has
+ * heterogeneous SMT topology.
+ */
+ if (max_smt_thread_num && max_smt_thread_num != i)
+ pr_warn_once("Heterogeneous SMT topology is partly supported by SMT control\n");
+
+ max_smt_thread_num = max_t(unsigned int, max_smt_thread_num, i);
+
cpu = get_cpu_for_node(core);
if (cpu >= 0) {
if (!leaf) {
@@ -677,6 +692,18 @@ static int __init parse_socket(struct device_node *socket)
if (!has_socket)
ret = parse_cluster(socket, 0, -1, 0);

+ /*
+ * Notify the CPU framework of the SMT support. Initialize the
+ * max_smt_thread_num to 1 if no SMT support detected or failed
+ * to parse the topology. A thread number of 1 can be handled by
+ * the framework so we don't need to check max_smt_thread_num to
+ * see we support SMT or not.
+ */
+ if (!max_smt_thread_num || ret)
+ max_smt_thread_num = 1;
+
+ cpu_smt_set_num_threads(max_smt_thread_num, max_smt_thread_num);
+
return ret;
}

--
2.24.0