[PATCH 2/2] kernel/smp: Tell the user we're bringing up secondary CPUs

[Michael Ellerman]

Currently we don't print anything before starting to bring up secondary
CPUs. This can be confusing if it takes a long time to bring up the
secondaries, or if the kernel crashes while doing so and produces no
further output.

On x86 they work around this by detecting when the first secondary CPU
comes up and printing a message (see announce_cpu()). But doing it in
smp_init() is simpler and works for all arches.

Signed-off-by: Michael Ellerman <***@ellerman.id.au>
---
kernel/smp.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/kernel/smp.c b/kernel/smp.c
index 6f5696d260c8..6d9af104de37 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -552,6 +552,8 @@ void __init smp_init(void)
idle_threads_init();
cpuhp_threads_init();

+ pr_info("smp: Bringing up secondary CPUs ...\n");
+
/* FIXME: This should be done in userspace --RR */
for_each_present_cpu(cpu) {
if (num_online_cpus() >= setup_max_cpus)

[Borislav Petkov]

Currently after bringing up secondary CPUs all arches print "Brought up
%d CPUs". On x86 they also print the number of nodes that were brought
online.
It would be nice to also print the number of nodes on other arches.
Although we could override smp_announce() on the other ~10 NUMA aware
arches, it seems simpler to just always print the number of nodes. On
non-NUMA arches there is just always 1 node.
Having done that, smp_announce() is no longer weak, and seems small
enough to just pull directly into smp_init().
---
arch/x86/kernel/smpboot.c | 8 --------
kernel/smp.c | 11 +++++------
2 files changed, 5 insertions(+), 14 deletions(-)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 42a93621f5b0..7eb8dfa56d34 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -821,14 +821,6 @@ wakeup_secondary_cpu_via_init(int phys_apicid, unsigned long start_eip)
return (send_status | accept_status);
}
-void smp_announce(void)
-{
- int num_nodes = num_online_nodes();
-
- printk(KERN_INFO "x86: Booted up %d node%s, %d CPUs\n",
- num_nodes, (num_nodes > 1 ? "s" : ""), num_online_cpus());
-}
-
/* reduce the number of lines printed when booting a large cpu count system */
static void announce_cpu(int cpu, int apicid)
{
diff --git a/kernel/smp.c b/kernel/smp.c
index bba3b201668d..6f5696d260c8 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -543,15 +543,11 @@ void __init setup_nr_cpu_ids(void)
nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
}
-void __weak smp_announce(void)
-{
- printk(KERN_INFO "Brought up %d CPUs\n", num_online_cpus());
-}
-
/* Called by boot processor to activate the rest. */
void __init smp_init(void)
{
unsigned int cpu;
+ int num_nodes;
idle_threads_init();
cpuhp_threads_init();
@@ -564,8 +560,11 @@ void __init smp_init(void)
cpu_up(cpu);
}
+ num_nodes = num_online_nodes();
+ pr_info("smp: Brought up %d node%s, %d CPUs\n",
+ num_nodes, (num_nodes > 1 ? "s" : ""), num_online_cpus());

Please define pr_fmt for this file so that pr_info adds the prefix
automatically. I guess

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

at the top, before all the include directives should suffice.

Other than that, for both patches:

Reviewed-by: Borislav Petkov <***@suse.de>