[patch 0/2] i386: CPU hotplug related patch series

[patch 0/2] i386: CPU hotplug related patch series

[Ashok Raj]

Hi Andrew

Following series is replica of what i did for x86_64.

- Remove broadcast IPI for flat mode when CPU hotplug is enabled.
- Add option to choose broadcast or mask version via command line.
- hold call_lock to exclude upcomming cpu during a smp_call_function()
  progress.

Cheers,
Ashok Raj

[patch 1/2] i386: Dont use IPI broadcast when using cpu hotplug.

[Ashok Raj]

[-- Attachment #1: i386-dont-use-ipi-broadcast.patch --]
[-- Type: text/plain, Size: 3352 bytes --]

This patch introduces a startup parameter no_broadcast. When we 
enable CONFIG_HOTPLUG_CPU, we dont want to use broadcast shortcut as it
has ill effects on a offline cpu. If we issue broadcast, the IPI is also
delivered to offline cpus, or partially up cpu causing stale IPI's to be
handled, which is a problem and can cause undesirable effects.

Introduces a new startup cmdline option no_ipi_broadcast, that can be
switched at cmdline if necessary.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Shaohua Li <shaohua.li@intel.com>
----------------------------------------------------
 arch/i386/mach-default/setup.c           |   27 +++++++++++++++++++++++++++
 include/asm-i386/mach-default/mach_ipi.h |   27 +++++++++++++++++++++++++--
 2 files changed, 52 insertions(+), 2 deletions(-)

Index: linux-2.6.12-rc6-mm1/include/asm-i386/mach-default/mach_ipi.h
===================================================================
--- linux-2.6.12-rc6-mm1.orig/include/asm-i386/mach-default/mach_ipi.h
+++ linux-2.6.12-rc6-mm1/include/asm-i386/mach-default/mach_ipi.h
@@ -4,11 +4,34 @@
 void send_IPI_mask_bitmask(cpumask_t mask, int vector);
 void __send_IPI_shortcut(unsigned int shortcut, int vector);
 
+extern int no_broadcast;
+
 static inline void send_IPI_mask(cpumask_t mask, int vector)
 {
 	send_IPI_mask_bitmask(mask, vector);
 }
 
+static inline void __local_send_IPI_allbutself(int vector)
+{
+	if (no_broadcast) {
+		cpumask_t mask = cpu_online_map;
+		int this_cpu = get_cpu();
+
+		cpu_clear(this_cpu, mask);
+		send_IPI_mask(mask, vector);
+		put_cpu();
+	} else
+		__send_IPI_shortcut(APIC_DEST_ALLBUT, vector);
+}
+
+static inline void __local_send_IPI_all(int vector)
+{
+	if (no_broadcast)
+		send_IPI_mask(cpu_online_map, vector);
+	else
+		__send_IPI_shortcut(APIC_DEST_ALLINC, vector);
+}
+
 static inline void send_IPI_allbutself(int vector)
 {
 	/*
@@ -18,13 +41,13 @@ static inline void send_IPI_allbutself(i
 	if (!(num_online_cpus() > 1))
 		return;
 
-	__send_IPI_shortcut(APIC_DEST_ALLBUT, vector);
+	__local_send_IPI_allbutself(vector);
 	return;
 }
 
 static inline void send_IPI_all(int vector)
 {
-	__send_IPI_shortcut(APIC_DEST_ALLINC, vector);
+	__local_send_IPI_all(vector);
 }
 
 #endif /* __ASM_MACH_IPI_H */
Index: linux-2.6.12-rc6-mm1/arch/i386/mach-default/setup.c
===================================================================
--- linux-2.6.12-rc6-mm1.orig/arch/i386/mach-default/setup.c
+++ linux-2.6.12-rc6-mm1/arch/i386/mach-default/setup.c
@@ -10,6 +10,14 @@
 #include <asm/acpi.h>
 #include <asm/arch_hooks.h>
 
+#ifdef CONFIG_HOTPLUG_CPU
+#define DEFAULT_SEND_IPI	(1)
+#else
+#define DEFAULT_SEND_IPI	(0)
+#endif
+
+int no_broadcast=DEFAULT_SEND_IPI;
+
 /**
  * pre_intr_init_hook - initialisation prior to setting up interrupt vectors
  *
@@ -104,3 +112,22 @@ void __init mca_nmi_hook(void)
 	printk("NMI generated from unknown source!\n");
 }
 #endif
+
+static __init int no_ipi_broadcast(char *str)
+{
+	get_option(&str, &no_broadcast);
+	printk ("Using %s mode\n", no_broadcast ? "No IPI Broadcast" :
+											"IPI Broadcast");
+	return 1;
+}
+
+__setup("no_ipi_broadcast", no_ipi_broadcast);
+
+static int __init print_ipi_mode(void)
+{
+	printk ("Using IPI %s mode\n", no_broadcast ? "No-Shortcut" :
+											"Shortcut");
+	return 0;
+}
+
+late_initcall(print_ipi_mode);

--

[patch 2/2] i386: hold call_lock when updating cpu_online_map

[Ashok Raj]

[-- Attachment #1: i386-hold-call-lock-when-adding-to-onlinemap.patch --]
[-- Type: text/plain, Size: 2351 bytes --]

We need to hold call-lock when updating cpu-online-map to ensure
the newly upcoming cpu is excluded in an ongoing smp_call_function.

Signed-off-by: Ashok Raj <ashok.raj@intel.com>
Acked-by: Shaohua Li <shaohua.li@intel.com>
-------------------------------------------------
 arch/i386/kernel/smp.c     |   10 ++++++++++
 arch/i386/kernel/smpboot.c |   10 ++++++++++
 include/asm-i386/smp.h     |    2 ++
 3 files changed, 22 insertions(+)

Index: linux-2.6.12-rc6-mm1/arch/i386/kernel/smp.c
===================================================================
--- linux-2.6.12-rc6-mm1.orig/arch/i386/kernel/smp.c
+++ linux-2.6.12-rc6-mm1/arch/i386/kernel/smp.c
@@ -506,6 +506,16 @@ struct call_data_struct {
 	int wait;
 };
 
+void lock_ipi_call_lock(void)
+{
+	spin_lock_irq(&call_lock);
+}
+
+void unlock_ipi_call_lock(void)
+{
+	spin_unlock_irq(&call_lock);
+}
+
 static struct call_data_struct * call_data;
 
 /*
Index: linux-2.6.12-rc6-mm1/include/asm-i386/smp.h
===================================================================
--- linux-2.6.12-rc6-mm1.orig/include/asm-i386/smp.h
+++ linux-2.6.12-rc6-mm1/include/asm-i386/smp.h
@@ -42,6 +42,8 @@ extern void smp_message_irq(int cpl, voi
 extern void smp_invalidate_rcv(void);		/* Process an NMI */
 extern void (*mtrr_hook) (void);
 extern void zap_low_mappings (void);
+extern void lock_ipi_call_lock(void);
+extern void unlock_ipi_call_lock(void);
 
 #define MAX_APICID 256
 extern u8 x86_cpu_to_apicid[];
Index: linux-2.6.12-rc6-mm1/arch/i386/kernel/smpboot.c
===================================================================
--- linux-2.6.12-rc6-mm1.orig/arch/i386/kernel/smpboot.c
+++ linux-2.6.12-rc6-mm1/arch/i386/kernel/smpboot.c
@@ -503,7 +503,17 @@ static void __devinit start_secondary(vo
 	set_cpu_sibling_map(raw_smp_processor_id());
 	wmb();
 
+	/*
+	 * We need to hold call_lock, so there is no inconsistency
+	 * between the time smp_call_function() determines number of
+	 * IPI receipients, and the time when the determination is made
+	 * for which cpus receive the IPI. Holding this
+	 * lock helps us to not include this cpu in a currently in progress
+	 * smp_call_function().
+	 */
+	lock_ipi_call_lock();
 	cpu_set(smp_processor_id(), cpu_online_map);
+	unlock_ipi_call_lock();
 
 	/* We can take interrupts now: we're officially "up". */
 	local_irq_enable();

--