For kexec -p, after boot_cpuid is mapping into the range of [0,
threads_per_core), then if nr_cpus is small, we will have the bitmap
[0,..., nr_cpus, ..., boot_cpuid, ...). This patch chooses cpus inside
the range of [boot_cpuid - nr_cpus +1, ..., boot_cpuid] to be online.
With this patch and the next, on a P9 machine with thread_per_core=4,
and set nr_cpus=2 for the crash kernel.
After
taskset -c 11 sh -c "echo c > /proc/sysrq-trigger"
Then
kdump:/sys/devices/system/cpu# cat possible
2-3
kdump:/sys/devices/system/cpu# cat present
2-3
kdump:/sys/devices/system/cpu# cat online
2-3
Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
---
arch/powerpc/kernel/setup-common.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c
index a683ed1..f3aaf9f 100644
--- a/arch/powerpc/kernel/setup-common.c
+++ b/arch/powerpc/kernel/setup-common.c
@@ -468,6 +468,7 @@ void __init smp_setup_cpu_maps(void)
int online_num = 0;
int next_cpu = boot_dn_nthreads;
bool btdn_handled = false;
+ int first_threadid = 0;
DBG("smp_setup_cpu_maps()\n");
@@ -497,7 +498,12 @@ void __init smp_setup_cpu_maps(void)
if (boot_cpuid < nthreads &&
be32_to_cpu(intserv[boot_cpuid]) == boot_cpuhwid) {
- cpu = 0;
+ /* choose a bunch of continous threads */
+ if (boot_cpuid > nr_cpu_ids - 1) {
+ first_threadid = boot_cpuid - nr_cpu_ids + 1;
+ }
+ /* keep the mapping of logical and thread */
+ cpu = first_threadid;
btdn_handled = true;
} else if ( !btdn_handled &&
nr_cpu_ids - online_num <= boot_dn_nthreads)
@@ -509,7 +515,8 @@ void __init smp_setup_cpu_maps(void)
}
- for (j = 0; j < nthreads && online_num < nr_cpu_ids; j++) {
+ for (j = first_threadid;
+ j < nthreads && online_num < nr_cpu_ids; j++) {
bool avail;
DBG(" thread %d -> cpu %d (hard id %d)\n",
--
2.7.4
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