From: Andrew Theurer <habanero@us.ibm.com>
The patch allows you to not boot a cpu with a specific apicid. This is an
enhancement over maxcpus. The problem with max cpus is that it does not
give you control over which specific cpus are not booted. This becomes a
problem with hyperthreading in situations when you only want the logical
processors from the N out of 8 physical cpus. The problem is that smp
ordering on some arches is not ideal for this, and can cause a cpu sibling
map like:
0:8
1:9
2:10
2:11
3:12
4:13
5:14
6:15
7:16
If you wanted both siblings on the the first 4 cpus in this system, maxcpus
will not work. Specifying maxcpus=8 would get you one sibling from all 8
physical cpus.
To fix this, simply use skip_apicids=x,y,z kernel parameter. This allows
basically any combination of cpus. You can even boot physical cpus with
different sibling counts on the same system for kicks.
Documentation/kernel-parameters.txt | 4 ++++
arch/i386/kernel/smpboot.c | 16 ++++++++++++++++
init/main.c | 14 ++++++++++++++
3 files changed, 34 insertions(+)
diff -puN arch/i386/kernel/smpboot.c~skip-apic-ids-on-boot arch/i386/kernel/smpboot.c
--- 25/arch/i386/kernel/smpboot.c~skip-apic-ids-on-boot 2003-06-26 18:38:18.000000000 -0700
+++ 25-akpm/arch/i386/kernel/smpboot.c 2003-06-26 18:38:18.000000000 -0700
@@ -82,6 +82,10 @@ extern unsigned char trampoline_data [];
extern unsigned char trampoline_end [];
static unsigned char *trampoline_base;
+/* used to selectively not boot certain CPUs with apicids */
+extern int skip_apic_ids[NR_CPUS];
+
+
/*
* Currently trivial. Write the real->protected mode
* bootstrap into the page concerned. The caller
@@ -934,6 +938,16 @@ void *xquad_portio;
int cpu_sibling_map[NR_CPUS] __cacheline_aligned;
+static int skip_this_apicid(int apicid)
+{
+ int i;
+
+ for (i = 1; i < (skip_apic_ids[0] + 1); i++)
+ if (apicid == skip_apic_ids[i])
+ return 1;
+ return 0;
+}
+
static void __init smp_boot_cpus(unsigned int max_cpus)
{
int apicid, cpu, bit, kicked;
@@ -1032,6 +1046,8 @@ static void __init smp_boot_cpus(unsigne
continue;
if (max_cpus <= cpucount+1)
continue;
+ if (skip_this_apicid(apicid))
+ continue;
if (do_boot_cpu(apicid))
printk("CPU #%d not responding - cannot use it.\n",
diff -puN Documentation/kernel-parameters.txt~skip-apic-ids-on-boot Documentation/kernel-parameters.txt
--- 25/Documentation/kernel-parameters.txt~skip-apic-ids-on-boot 2003-06-26 18:38:18.000000000 -0700
+++ 25-akpm/Documentation/kernel-parameters.txt 2003-06-26 18:38:18.000000000 -0700
@@ -886,6 +886,10 @@ running once the system is up.
Format: <io>,<irq>,<dma>
See header of drivers/cdrom/sjcd.c.
+ skip_apicids= [SMP]
+ Format: <apic1>[,<apic2>[,...,<apicN>]]
+ Do not boot cpus with matching apicid.
+
slram= [HW,MTD]
smart2= [HW]
diff -puN init/main.c~skip-apic-ids-on-boot init/main.c
--- 25/init/main.c~skip-apic-ids-on-boot 2003-06-26 18:38:18.000000000 -0700
+++ 25-akpm/init/main.c 2003-06-26 18:38:18.000000000 -0700
@@ -115,6 +115,8 @@ char *execute_command;
/* Setup configured maximum number of CPUs to activate */
static unsigned int max_cpus = NR_CPUS;
+/* Don't boot apicids in this list */
+int skip_apic_ids[NR_CPUS];
/*
* Setup routine for controlling SMP activation
@@ -142,6 +144,18 @@ static int __init maxcpus(char *str)
__setup("maxcpus=", maxcpus);
+static int __init skip_apicids(char *str)
+{
+ int i;
+
+ get_options(str, NR_CPUS, skip_apic_ids);
+ for (i = 1; i < (skip_apic_ids[0]+1); i++)
+ printk( "CPU with apicid %i will not be booted\n", skip_apic_ids[i]);
+ return 1;
+}
+
+__setup("skip_apicids=", skip_apicids);
+
static char * argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
char * envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
_