In the current code, SMP is selected in Kconfig for LoongArch, the users
can not unset it, this is reasonable for a multiprocessor machine. But as
the help info of config SMP said, if you have a system with only one CPU,
say N. On a uniprocessor machine, the kernel will run faster if you say N
here.
The Loongson-2K0500 is a single-core CPU for applications like industrial
control, printing terminals, and BMC (Baseboard Management Controller),
there are many development boards, products and solutions on the market,
so it is better and necessary to give a chance to build under !CONFIG_SMP
for a uniprocessor machine.
First of all, do not select SMP for config LOONGARCH in Kconfig to make it
possible to unset CONFIG_SMP. Then, do some changes to fix the warnings and
errors if CONFIG_SMP is not set.
(1) Define get_ipi_irq() only if CONFIG_SMP is set to fix the warning:
arch/loongarch/kernel/irq.c:90:19: warning: 'get_ipi_irq' defined but not used [-Wunused-function]
(2) Add "#ifdef CONFIG_SMP" in asm/smp.h to fix the warning:
/arch/loongarch/include/asm/smp.h:49:9: warning: "raw_smp_processor_id" redefined
49 | #define raw_smp_processor_id raw_smp_processor_id
| ^~~~~~~~~~~~~~~~~~~~
/include/linux/smp.h:198:9: note: this is the location of the previous definition
198 | #define raw_smp_processor_id() 0
(3) Define machine_shutdown() as empty under !CONFIG_SMP to fix the error:
arch/loongarch/kernel/machine_kexec.c: In function 'machine_shutdown':
arch/loongarch/kernel/machine_kexec.c:233:25: error: implicit declaration of function 'cpu_device_up'; did you mean 'put_device'? [-Wimplicit-function-declaration]
(4) Make config SCHED_SMT depends on SMP to fix many errors such as:
kernel/sched/core.c: In function 'sched_core_find':
kernel/sched/core.c:310:43: error: 'struct rq' has no member named 'cpu'
(5) Define cpu_logical_map(cpu) as read_csr_cpuid() under !CONFIG_SMP
in asm/smp.h and then include asm/smp.h in asm/acpi.h (because acpi.h
is included in linux/irq.h indirectly) to fix many build errors under
drivers/irqchip such as:
drivers/irqchip/irq-loongson-eiointc.c: In function 'cpu_to_eio_node':
drivers/irqchip/irq-loongson-eiointc.c:59:16: error: implicit declaration of function 'cpu_logical_map' [-Wimplicit-function-declaration]
When running the UnixBench tests with "-c 1" single-streamed pass,
the improvement in performance is about 9 percent with this patch.
By the way, it is helpful to debug and analysis the kernel issue
of multi-core system under !CONFIG_SMP.
Signed-off-by: Tiezhu Yang <[email protected]>
---
arch/loongarch/Kconfig | 2 +-
arch/loongarch/include/asm/acpi.h | 1 +
arch/loongarch/include/asm/smp.h | 5 +++++
arch/loongarch/kernel/irq.c | 2 ++
arch/loongarch/kernel/machine_kexec.c | 2 +-
5 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 64052ae2c2af..8946945daf34 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -174,7 +174,6 @@ config LOONGARCH
select PCI_QUIRKS
select PERF_USE_VMALLOC
select RTC_LIB
- select SMP
select SPARSE_IRQ
select SYSCTL_ARCH_UNALIGN_ALLOW
select SYSCTL_ARCH_UNALIGN_NO_WARN
@@ -420,6 +419,7 @@ config EFI_STUB
config SCHED_SMT
bool "SMT scheduler support"
+ depends on SMP
default y
help
Improves scheduler's performance when there are multiple
diff --git a/arch/loongarch/include/asm/acpi.h b/arch/loongarch/include/asm/acpi.h
index a4ad3f75bd60..5174063ad08e 100644
--- a/arch/loongarch/include/asm/acpi.h
+++ b/arch/loongarch/include/asm/acpi.h
@@ -8,6 +8,7 @@
#ifndef _ASM_LOONGARCH_ACPI_H
#define _ASM_LOONGARCH_ACPI_H
+#include <asm/smp.h>
#include <asm/suspend.h>
#ifdef CONFIG_ACPI
diff --git a/arch/loongarch/include/asm/smp.h b/arch/loongarch/include/asm/smp.h
index f81e5f01d619..1ec11b57e60c 100644
--- a/arch/loongarch/include/asm/smp.h
+++ b/arch/loongarch/include/asm/smp.h
@@ -6,6 +6,7 @@
#ifndef __ASM_SMP_H
#define __ASM_SMP_H
+#ifdef CONFIG_SMP
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/linkage.h>
@@ -101,4 +102,8 @@ static inline void __cpu_die(unsigned int cpu)
}
#endif
+#else /* !CONFIG_SMP */
+#define cpu_logical_map(cpu) read_csr_cpuid()
+#endif /* CONFIG_SMP */
+
#endif /* __ASM_SMP_H */
diff --git a/arch/loongarch/kernel/irq.c b/arch/loongarch/kernel/irq.c
index 883e5066ae44..e791fa275ec5 100644
--- a/arch/loongarch/kernel/irq.c
+++ b/arch/loongarch/kernel/irq.c
@@ -87,6 +87,7 @@ static void __init init_vec_parent_group(void)
acpi_table_parse(ACPI_SIG_MCFG, early_pci_mcfg_parse);
}
+#ifdef CONFIG_SMP
static int __init get_ipi_irq(void)
{
struct irq_domain *d = irq_find_matching_fwnode(cpuintc_handle, DOMAIN_BUS_ANY);
@@ -96,6 +97,7 @@ static int __init get_ipi_irq(void)
return -EINVAL;
}
+#endif
void __init init_IRQ(void)
{
diff --git a/arch/loongarch/kernel/machine_kexec.c b/arch/loongarch/kernel/machine_kexec.c
index 2dcb9e003657..8ae641dc53bb 100644
--- a/arch/loongarch/kernel/machine_kexec.c
+++ b/arch/loongarch/kernel/machine_kexec.c
@@ -225,6 +225,7 @@ void crash_smp_send_stop(void)
void machine_shutdown(void)
{
+#ifdef CONFIG_SMP
int cpu;
/* All CPUs go to reboot_code_buffer */
@@ -232,7 +233,6 @@ void machine_shutdown(void)
if (!cpu_online(cpu))
cpu_device_up(get_cpu_device(cpu));
-#ifdef CONFIG_SMP
smp_call_function(kexec_shutdown_secondary, NULL, 0);
#endif
}
--
2.42.0