smp_processor_id() accesses the per-cpu variable, so the compiler
is not able to move the call after the early exit on its own.
Also rename "cpu" variable to a more descriptive "this_cpu".
No functional change intended.
Cc: Dave Hansen <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
v2: Split from v1 patch.
---
arch/x86/kernel/smp.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 96a771f9f930..97f6f0cbb43a 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -148,14 +148,15 @@ static int register_stop_handler(void)
static void native_stop_other_cpus(int wait)
{
- unsigned int cpu = smp_processor_id();
+ unsigned int this_cpu;
unsigned long flags, timeout;
if (reboot_force)
return;
/* Only proceed if this is the first CPU to reach this code */
- if (atomic_cmpxchg(&stopping_cpu, -1, cpu) != -1)
+ this_cpu = smp_processor_id();
+ if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
return;
/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */
@@ -186,7 +187,7 @@ static void native_stop_other_cpus(int wait)
* NMIs.
*/
cpumask_copy(&cpus_stop_mask, cpu_online_mask);
- cpumask_clear_cpu(cpu, &cpus_stop_mask);
+ cpumask_clear_cpu(this_cpu, &cpus_stop_mask);
if (!cpumask_empty(&cpus_stop_mask)) {
apic_send_IPI_allbutself(REBOOT_VECTOR);
@@ -210,6 +211,8 @@ static void native_stop_other_cpus(int wait)
* CPUs to stop.
*/
if (!smp_no_nmi_ipi && !register_stop_handler()) {
+ unsigned int cpu;
+
pr_emerg("Shutting down cpus with NMI\n");
for_each_cpu(cpu, &cpus_stop_mask)
--
2.42.0
Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old.
X86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after CMPXCHG.
Tested by building a native Fedora-38 kernel and rebooting
a 12-way SMP system using "shutdown -r" command some 100 times.
No functional change intended.
Cc: Dave Hansen <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Signed-off-by: Uros Bizjak <[email protected]>
---
v2: Split from v1 patch. Simplify commit entry and state
how the patch was tested.
---
arch/x86/kernel/smp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 97f6f0cbb43a..2908e063d7d8 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -148,15 +148,16 @@ static int register_stop_handler(void)
static void native_stop_other_cpus(int wait)
{
- unsigned int this_cpu;
+ unsigned int old_cpu, this_cpu;
unsigned long flags, timeout;
if (reboot_force)
return;
/* Only proceed if this is the first CPU to reach this code */
+ old_cpu = -1;
this_cpu = smp_processor_id();
- if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
+ if (!atomic_try_cmpxchg(&stopping_cpu, &old_cpu, this_cpu))
return;
/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */
--
2.42.0
The following commit has been merged into the x86/percpu branch of tip:
Commit-ID: 9d1c8f21533729b6ead531b676fa7d327cf00819
Gitweb: https://git.kernel.org/tip/9d1c8f21533729b6ead531b676fa7d327cf00819
Author: Uros Bizjak <[email protected]>
AuthorDate: Thu, 23 Nov 2023 21:34:22 +01:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Thu, 30 Nov 2023 20:25:09 +01:00
x86/smp: Move the call to smp_processor_id() after the early exit in native_stop_other_cpus()
Improve code generation in native_stop_other_cpus() a tiny bit:
smp_processor_id() accesses a per-CPU variable, so the compiler
is not able to move the call after the early exit on its own.
Also rename the "cpu" variable to a more descriptive "this_cpu", and
use 'cpu' as a separate iterator variable later in the function.
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/kernel/smp.c | 9 ++++++---
1 file changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 6eb06d0..65dd44e 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -148,14 +148,15 @@ static int register_stop_handler(void)
static void native_stop_other_cpus(int wait)
{
- unsigned int cpu = smp_processor_id();
+ unsigned int this_cpu;
unsigned long flags, timeout;
if (reboot_force)
return;
/* Only proceed if this is the first CPU to reach this code */
- if (atomic_cmpxchg(&stopping_cpu, -1, cpu) != -1)
+ this_cpu = smp_processor_id();
+ if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
return;
/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */
@@ -190,7 +191,7 @@ static void native_stop_other_cpus(int wait)
* NMIs.
*/
cpumask_copy(&cpus_stop_mask, cpu_online_mask);
- cpumask_clear_cpu(cpu, &cpus_stop_mask);
+ cpumask_clear_cpu(this_cpu, &cpus_stop_mask);
if (!cpumask_empty(&cpus_stop_mask)) {
apic_send_IPI_allbutself(REBOOT_VECTOR);
@@ -234,6 +235,8 @@ static void native_stop_other_cpus(int wait)
* CPUs to stop.
*/
if (!smp_no_nmi_ipi && !register_stop_handler()) {
+ unsigned int cpu;
+
pr_emerg("Shutting down cpus with NMI\n");
for_each_cpu(cpu, &cpus_stop_mask)
The following commit has been merged into the x86/percpu branch of tip:
Commit-ID: 9e9d673b2c84719937db5d6ab1d8cbcd7d45e974
Gitweb: https://git.kernel.org/tip/9e9d673b2c84719937db5d6ab1d8cbcd7d45e974
Author: Uros Bizjak <[email protected]>
AuthorDate: Thu, 23 Nov 2023 21:34:23 +01:00
Committer: Ingo Molnar <[email protected]>
CommitterDate: Thu, 30 Nov 2023 20:25:09 +01:00
x86/smp: Use atomic_try_cmpxchg in native_stop_other_cpus()
Use atomic_try_cmpxchg() instead of atomic_cmpxchg(*ptr, old, new) == old.
X86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after the CMPXCHG.
Tested by building a native Fedora-38 kernel and rebooting
a 12-way SMP system using "shutdown -r" command some 100 times.
No functional change intended.
Signed-off-by: Uros Bizjak <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
arch/x86/kernel/smp.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index 65dd44e..1bb7952 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -148,15 +148,16 @@ static int register_stop_handler(void)
static void native_stop_other_cpus(int wait)
{
- unsigned int this_cpu;
+ unsigned int old_cpu, this_cpu;
unsigned long flags, timeout;
if (reboot_force)
return;
/* Only proceed if this is the first CPU to reach this code */
+ old_cpu = -1;
this_cpu = smp_processor_id();
- if (atomic_cmpxchg(&stopping_cpu, -1, this_cpu) != -1)
+ if (!atomic_try_cmpxchg(&stopping_cpu, &old_cpu, this_cpu))
return;
/* For kexec, ensure that offline CPUs are out of MWAIT and in HLT */