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Subject[PATCH 3/4] cpumask: use maxcpus=NUM to extend the cpu limit as well as restrict the limit
Impact: allow adding additional cpus.

Use maxcpus=NUM kernel parameter to extend the number of possible cpus as well
as (currently) limit them. Any cpus >= number of present cpus will disabled.

The ability to HOTPLUG ON cpus that are "possible" but not "present" is
dealt with in a later patch.

Based on:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
+ git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git/cpus4096
+ git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-ingo.git

Signed-off-by: Mike Travis <travis@sgi.com>
---
Documentation/kernel-parameters.txt | 6 +++++-
arch/x86/kernel/alternative.c | 2 +-
arch/x86/kernel/apic.c | 12 +++++++++---
arch/x86/kernel/smpboot.c | 18 ++++++++++++++----
arch/x86/kernel/visws_quirks.c | 4 ++--
include/linux/smp.h | 19 ++++++++++++++++++-
init/main.c | 14 ++++++--------
7 files changed, 55 insertions(+), 20 deletions(-)
--- linux-2.6-for-ingo.orig/Documentation/kernel-parameters.txt
+++ linux-2.6-for-ingo/Documentation/kernel-parameters.txt
@@ -1201,7 +1201,11 @@ and is between 256 and 4096 characters.
should make use of. maxcpus=n : n >= 0 limits the
kernel to using 'n' processors. n=0 is a special case,
it is equivalent to "nosmp", which also disables
- the IO APIC.
+ the IO APIC. On [X86] maxcpus can also be used to
+ extend the number of possible cpus to overcome ACPI
+ tables that do not indicate disabled cpus, as well as
+ allow for additional cpus to be HOT PLUGGED in.
+ Format: <0-NR_CPUS>

max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater than
or equal to this physical address is ignored.
--- linux-2.6-for-ingo.orig/arch/x86/kernel/alternative.c
+++ linux-2.6-for-ingo/arch/x86/kernel/alternative.c
@@ -444,7 +444,7 @@ void __init alternative_instructions(voi
_text, _etext);

/* Only switch to UP mode if we don't immediately boot others */
- if (num_present_cpus() == 1 || setup_max_cpus <= 1)
+ if (num_present_cpus() == 1 || maxcpus() <= 1)
alternatives_smp_switch(0);
}
#endif
--- linux-2.6-for-ingo.orig/arch/x86/kernel/apic.c
+++ linux-2.6-for-ingo/arch/x86/kernel/apic.c
@@ -1845,9 +1845,15 @@ void __cpuinit generic_processor_info(in
}
apic_version[apicid] = version;

- if (num_processors >= NR_CPUS) {
- printk(KERN_WARNING "WARNING: NR_CPUS limit of %i reached."
- " Processor ignored.\n", NR_CPUS);
+ if (num_processors >= maxcpus()) {
+ int max = maxcpus();
+ int thiscpu = max + disabled_cpus;
+
+ printk(KERN_WARNING
+ "ACPI: NR_CPUS/maxcpus limit of %i reached."
+ " Processor %d/0x%x ignored.\n", max, thiscpu, apicid);
+
+ disabled_cpus++;
return;
}

--- linux-2.6-for-ingo.orig/arch/x86/kernel/smpboot.c
+++ linux-2.6-for-ingo/arch/x86/kernel/smpboot.c
@@ -1266,7 +1266,7 @@ void __init native_smp_cpus_done(unsigne
*
* Three ways to find out the number of additional hotplug CPUs:
* - If the BIOS specified disabled CPUs in ACPI/mptables use that.
- * - The user can overwrite it with additional_cpus=NUM
+ * - The user can overwrite it with maxcpus=NUM
* - Otherwise don't reserve additional CPUs.
* We do this because additional CPUs waste a lot of memory.
* -AK
@@ -1279,9 +1279,19 @@ __init void prefill_possible_map(void)
if (!num_processors)
num_processors = 1;

- possible = num_processors + disabled_cpus;
- if (possible > NR_CPUS)
- possible = NR_CPUS;
+ if (setup_max_cpus == -1) /* not specified */
+ possible = num_processors + disabled_cpus;
+ else if (setup_max_cpus == 0) /* UP mode forced */
+ possible = 1;
+ else /* user specified */
+ possible = setup_max_cpus;
+
+ if (possible > CONFIG_NR_CPUS) {
+ printk(KERN_WARNING
+ "%d Processors exceeds NR_CPUS limit of %d\n",
+ possible, CONFIG_NR_CPUS);
+ possible = CONFIG_NR_CPUS;
+ }

printk(KERN_INFO "SMP: Allowing %d CPUs, %d hotplug CPUs\n",
possible, max_t(int, possible - num_processors, 0));
--- linux-2.6-for-ingo.orig/arch/x86/kernel/visws_quirks.c
+++ linux-2.6-for-ingo/arch/x86/kernel/visws_quirks.c
@@ -228,8 +228,8 @@ static int __init visws_find_smp_config(
ncpus = CO_CPU_MAX;
}

- if (ncpus > setup_max_cpus)
- ncpus = setup_max_cpus;
+ if (ncpus > maxcpus())
+ ncpus = maxcpus();

#ifdef CONFIG_X86_LOCAL_APIC
smp_found_config = 1;
--- linux-2.6-for-ingo.orig/include/linux/smp.h
+++ linux-2.6-for-ingo/include/linux/smp.h
@@ -112,7 +112,18 @@ int on_each_cpu(void (*func) (void *info
*/
void smp_prepare_boot_cpu(void);

-extern unsigned int setup_max_cpus;
+extern int setup_max_cpus;
+static inline int maxcpus(void)
+{
+ int maxcpus = setup_max_cpus;
+
+ if (maxcpus == -1 || maxcpus > CONFIG_NR_CPUS)
+ maxcpus = CONFIG_NR_CPUS;
+ else if (maxcpus == 0)
+ maxcpus = 1;
+
+ return maxcpus;
+}

#else /* !SMP */

@@ -149,6 +160,12 @@ static inline void smp_send_reschedule(i
static inline void init_call_single_data(void)
{
}
+
+static inline int maxcpus(void)
+{
+ return 1;
+}
+
#endif /* !SMP */

/*
--- linux-2.6-for-ingo.orig/init/main.c
+++ linux-2.6-for-ingo/init/main.c
@@ -132,7 +132,7 @@ static char *ramdisk_execute_command;

#ifdef CONFIG_SMP
/* Setup configured maximum number of CPUs to activate */
-unsigned int __initdata setup_max_cpus = NR_CPUS;
+int setup_max_cpus = -1;

/*
* Setup routine for controlling SMP activation
@@ -157,7 +157,7 @@ static int __init nosmp(char *str)

early_param("nosmp", nosmp);

-static int __init maxcpus(char *str)
+static int __init set_maxcpus(char *str)
{
get_option(&str, &setup_max_cpus);
if (setup_max_cpus == 0)
@@ -166,9 +166,7 @@ static int __init maxcpus(char *str)
return 0;
}

-early_param("maxcpus", maxcpus);
-#else
-#define setup_max_cpus NR_CPUS
+early_param("maxcpus", set_maxcpus);
#endif

/*
@@ -425,7 +423,7 @@ static void __init smp_init(void)

/* FIXME: This should be done in userspace --RR */
for_each_present_cpu(cpu) {
- if (num_online_cpus() >= setup_max_cpus)
+ if (num_online_cpus() >= maxcpus())
break;
if (!cpu_online(cpu))
cpu_up(cpu);
@@ -433,7 +431,7 @@ static void __init smp_init(void)

/* Any cleanup work */
printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
- smp_cpus_done(setup_max_cpus);
+ smp_cpus_done(maxcpus());
}

#endif
@@ -857,7 +855,7 @@ static int __init kernel_init(void * unu

cad_pid = task_pid(current);

- smp_prepare_cpus(setup_max_cpus);
+ smp_prepare_cpus(maxcpus());

do_pre_smp_initcalls();
start_boot_trace();


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