[PATCH] s390: additional_cpus parameter

Introduce additional_cpus command line option. By default no additional cpu
can be attached to the system anymore. Only the cpus present at IPL time can
be switched on/off. If it is desired that additional cpus can be attached to
the system the maximum number of additional cpus needs to be specified with
this option.

This change is necessary in order to limit the waste of per_cpu data
structures.

Signed-off-by: Heiko Carstens <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/cpu-hotplug.txt

···
 			Joel Schopp <[e-mail]>
 		ia64/x86_64:
 			Ashok Raj <[e-mail]>
+		s390:
+			Heiko Carstens <[e-mail]>
 
 Authors: Ashok Raj <[e-mail]>
 Lots of feedback: Nathan Lynch <[e-mail]>,
···
              maxcpus=2 will only boot 2. You can choose to bring the
              other cpus later online, read FAQ's for more info.
 
-additional_cpus*=n	Use this to limit hotpluggable cpus. This option sets
-			cpu_possible_map = cpu_present_map + additional_cpus
-
-(*) Option valid only for following architectures
-- x86_64, ia64
+additional_cpus=n	[x86_64, s390 only] use this to limit hotpluggable cpus.
+                          This option sets
+  			cpu_possible_map = cpu_present_map + additional_cpus
 
 ia64 and x86_64 use the number of disabled local apics in ACPI tables MADT
 to determine the number of potentially hot-pluggable cpus. The implementation

arch/s390/kernel/setup.c

···
 	init_mm.brk = (unsigned long) &_end;
 
 	parse_cmdline_early(cmdline_p);
+	parse_early_param();
 
 	setup_memory();
 	setup_resources();
···
 
         cpu_init();
         __cpu_logical_map[0] = S390_lowcore.cpu_data.cpu_addr;
+	smp_setup_cpu_possible_map();
 
 	/*
 	 * Create kernel page tables and switch to virtual addressing.

arch/s390/kernel/smp.c

···
 /*
  *  arch/s390/kernel/smp.c
  *
- *  S390 version
- *    Copyright (C) 1999,2000 IBM Deutschland Entwicklung GmbH, IBM Corporation
+ *    Copyright (C) IBM Corp. 1999,2006
  *    Author(s): Denis Joseph Barrow ([e-mail],[e-mail]),
  *               Martin Schwidefsky ([e-mail])
  *               Heiko Carstens ([e-mail])
···
 #include <asm/cpcmd.h>
 #include <asm/tlbflush.h>
 
-/* prototypes */
-
 extern volatile int __cpu_logical_map[];
 
 /*
···
 
 struct _lowcore *lowcore_ptr[NR_CPUS];
 
-cpumask_t cpu_online_map;
-cpumask_t cpu_possible_map = CPU_MASK_ALL;
+cpumask_t cpu_online_map = CPU_MASK_NONE;
+cpumask_t cpu_possible_map = CPU_MASK_NONE;
 
 static struct task_struct *current_set[NR_CPUS];
-
-EXPORT_SYMBOL(cpu_online_map);
 
 /*
  * Reboot, halt and power_off routines for SMP.
···
  * Lets check how many CPUs we have.
  */
 
-void
-__init smp_check_cpus(unsigned int max_cpus)
+static unsigned int
+__init smp_count_cpus(void)
 {
-	int cpu, num_cpus;
+	unsigned int cpu, num_cpus;
 	__u16 boot_cpu_addr;
 
 	/*
···
 	boot_cpu_addr = S390_lowcore.cpu_data.cpu_addr;
 	current_thread_info()->cpu = 0;
 	num_cpus = 1;
-	for (cpu = 0; cpu <= 65535 && num_cpus < max_cpus; cpu++) {
+	for (cpu = 0; cpu <= 65535; cpu++) {
 		if ((__u16) cpu == boot_cpu_addr)
 			continue;
-		__cpu_logical_map[num_cpus] = (__u16) cpu;
-		if (signal_processor(num_cpus, sigp_sense) ==
+		__cpu_logical_map[1] = (__u16) cpu;
+		if (signal_processor(1, sigp_sense) ==
 		    sigp_not_operational)
 			continue;
-		cpu_set(num_cpus, cpu_present_map);
 		num_cpus++;
 	}
 
 	printk("Detected %d CPU's\n",(int) num_cpus);
 	printk("Boot cpu address %2X\n", boot_cpu_addr);
+
+	return num_cpus;
 }
 
 /*
···
 	return 0;
 }
 
+static unsigned int __initdata additional_cpus;
+
+void __init smp_setup_cpu_possible_map(void)
+{
+	unsigned int pcpus, cpu;
+
+	pcpus = smp_count_cpus() + additional_cpus;
+
+	if (pcpus > NR_CPUS)
+		pcpus = NR_CPUS;
+
+	for (cpu = 0; cpu < pcpus; cpu++)
+		cpu_set(cpu, cpu_possible_map);
+
+	cpu_present_map = cpu_possible_map;
+}
+
+#ifdef CONFIG_HOTPLUG_CPU
+
+static int __init setup_additional_cpus(char *s)
+{
+	additional_cpus = simple_strtoul(s, NULL, 0);
+	return 0;
+}
+early_param("additional_cpus", setup_additional_cpus);
+
 int
 __cpu_disable(void)
 {
···
 	for(;;);
 }
 
+#endif /* CONFIG_HOTPLUG_CPU */
+
 /*
  *	Cycle through the processors and setup structures.
  */
···
         /* request the 0x1201 emergency signal external interrupt */
         if (register_external_interrupt(0x1201, do_ext_call_interrupt) != 0)
                 panic("Couldn't request external interrupt 0x1201");
-        smp_check_cpus(max_cpus);
         memset(lowcore_ptr,0,sizeof(lowcore_ptr));  
         /*
          *  Initialize prefix pages and stacks for all possible cpus
···
 	BUG_ON(smp_processor_id() != 0);
 
 	cpu_set(0, cpu_online_map);
-	cpu_set(0, cpu_present_map);
 	S390_lowcore.percpu_offset = __per_cpu_offset[0];
 	current_set[0] = current;
 }
 
 void smp_cpus_done(unsigned int max_cpus)
 {
-	cpu_present_map = cpu_possible_map;
 }
 
 /*
···
 
 subsys_initcall(topology_init);
 
+EXPORT_SYMBOL(cpu_online_map);
 EXPORT_SYMBOL(cpu_possible_map);
 EXPORT_SYMBOL(lowcore_ptr);
 EXPORT_SYMBOL(smp_ctl_set_bit);

include/asm-s390/smp.h

···
 	__u16      cpu;
 } sigp_info;
 
+extern void smp_setup_cpu_possible_map(void);
 extern int smp_call_function_on(void (*func) (void *info), void *info,
 				int nonatomic, int wait, int cpu);
 #define NO_PROC_ID		0xFF		/* No processor magic marker */
···
 #define smp_cpu_not_running(cpu)	1
 #define smp_get_cpu(cpu) ({ 0; })
 #define smp_put_cpu(cpu) ({ 0; })
+#define smp_setup_cpu_possible_map()
 #endif
 
 #endif