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Message-ID: <156864062018.3407.12735658875708933630.tglx@nanos.tec.linutronix.de>
Date: Mon, 16 Sep 2019 13:30:20 -0000
From: Thomas Gleixner <tglx@...utronix.de>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org
Subject: [GIT pull] smp/hotplug for 5.4-rc1
Linus,
please pull the latest smp-hotplug-for-linus git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git smp-hotplug-for-linus
up to: 0c09ab96fc82: cpu/hotplug: Cache number of online CPUs
A small update for the SMP hotplug code code:
- Track bootet once CPUs in a cpumask so the x86 APIC code has an easy
way to decide whether broadcast IPIs are safe to use or not.
- Implement a cpumask_or_equal() helper for the IPI broadcast evaluation.
The above two changes have been also pulled into the x86/apic branch
for implementing the conditional IPI broadcast feature.
- Cache the number of online CPUs instead of reevaluating it over and
over. num_online_cpus() is an unreliable snapshot anyway except when it
is used outside a cpu hotplug locked region. The cached access is not
changing this, but it's definitely faster than calculating the bitmap
wheight especially in hot pathes.
Thanks,
tglx
------------------>
Thomas Gleixner (3):
smp/hotplug: Track booted once CPUs in a cpumask
cpumask: Implement cpumask_or_equal()
cpu/hotplug: Cache number of online CPUs
include/linux/bitmap.h | 23 +++++++++++++++++++++++
include/linux/cpumask.h | 41 ++++++++++++++++++++++++++++++++---------
kernel/cpu.c | 35 +++++++++++++++++++++++++++++++----
lib/bitmap.c | 20 ++++++++++++++++++++
4 files changed, 106 insertions(+), 13 deletions(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index f58e97446abc..90528f12bdfa 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -120,6 +120,10 @@ extern int __bitmap_empty(const unsigned long *bitmap, unsigned int nbits);
extern int __bitmap_full(const unsigned long *bitmap, unsigned int nbits);
extern int __bitmap_equal(const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int nbits);
+extern bool __pure __bitmap_or_equal(const unsigned long *src1,
+ const unsigned long *src2,
+ const unsigned long *src3,
+ unsigned int nbits);
extern void __bitmap_complement(unsigned long *dst, const unsigned long *src,
unsigned int nbits);
extern void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
@@ -321,6 +325,25 @@ static inline int bitmap_equal(const unsigned long *src1,
return __bitmap_equal(src1, src2, nbits);
}
+/**
+ * bitmap_or_equal - Check whether the or of two bitnaps is equal to a third
+ * @src1: Pointer to bitmap 1
+ * @src2: Pointer to bitmap 2 will be or'ed with bitmap 1
+ * @src3: Pointer to bitmap 3. Compare to the result of *@...1 | *@...2
+ *
+ * Returns: True if (*@...1 | *@...2) == *@...3, false otherwise
+ */
+static inline bool bitmap_or_equal(const unsigned long *src1,
+ const unsigned long *src2,
+ const unsigned long *src3,
+ unsigned int nbits)
+{
+ if (!small_const_nbits(nbits))
+ return __bitmap_or_equal(src1, src2, src3, nbits);
+
+ return !(((*src1 | *src2) ^ *src3) & BITMAP_LAST_WORD_MASK(nbits));
+}
+
static inline int bitmap_intersects(const unsigned long *src1,
const unsigned long *src2, unsigned int nbits)
{
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 21755471b1c3..b5a5a1ed9efd 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -10,6 +10,7 @@
#include <linux/kernel.h>
#include <linux/threads.h>
#include <linux/bitmap.h>
+#include <linux/atomic.h>
#include <linux/bug.h>
/* Don't assign or return these: may not be this big! */
@@ -95,8 +96,21 @@ extern struct cpumask __cpu_active_mask;
#define cpu_present_mask ((const struct cpumask *)&__cpu_present_mask)
#define cpu_active_mask ((const struct cpumask *)&__cpu_active_mask)
+extern atomic_t __num_online_cpus;
+
#if NR_CPUS > 1
-#define num_online_cpus() cpumask_weight(cpu_online_mask)
+/**
+ * num_online_cpus() - Read the number of online CPUs
+ *
+ * Despite the fact that __num_online_cpus is of type atomic_t, this
+ * interface gives only a momentary snapshot and is not protected against
+ * concurrent CPU hotplug operations unless invoked from a cpuhp_lock held
+ * region.
+ */
+static inline unsigned int num_online_cpus(void)
+{
+ return atomic_read(&__num_online_cpus);
+}
#define num_possible_cpus() cpumask_weight(cpu_possible_mask)
#define num_present_cpus() cpumask_weight(cpu_present_mask)
#define num_active_cpus() cpumask_weight(cpu_active_mask)
@@ -115,6 +129,8 @@ extern struct cpumask __cpu_active_mask;
#define cpu_active(cpu) ((cpu) == 0)
#endif
+extern cpumask_t cpus_booted_once_mask;
+
static inline void cpu_max_bits_warn(unsigned int cpu, unsigned int bits)
{
#ifdef CONFIG_DEBUG_PER_CPU_MAPS
@@ -473,6 +489,20 @@ static inline bool cpumask_equal(const struct cpumask *src1p,
nr_cpumask_bits);
}
+/**
+ * cpumask_or_equal - *src1p | *src2p == *src3p
+ * @src1p: the first input
+ * @src2p: the second input
+ * @src3p: the third input
+ */
+static inline bool cpumask_or_equal(const struct cpumask *src1p,
+ const struct cpumask *src2p,
+ const struct cpumask *src3p)
+{
+ return bitmap_or_equal(cpumask_bits(src1p), cpumask_bits(src2p),
+ cpumask_bits(src3p), nr_cpumask_bits);
+}
+
/**
* cpumask_intersects - (*src1p & *src2p) != 0
* @src1p: the first input
@@ -805,14 +835,7 @@ set_cpu_present(unsigned int cpu, bool present)
cpumask_clear_cpu(cpu, &__cpu_present_mask);
}
-static inline void
-set_cpu_online(unsigned int cpu, bool online)
-{
- if (online)
- cpumask_set_cpu(cpu, &__cpu_online_mask);
- else
- cpumask_clear_cpu(cpu, &__cpu_online_mask);
-}
+void set_cpu_online(unsigned int cpu, bool online);
static inline void
set_cpu_active(unsigned int cpu, bool active)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index e84c0873559e..e1967e9eddc2 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -62,7 +62,6 @@ struct cpuhp_cpu_state {
bool rollback;
bool single;
bool bringup;
- bool booted_once;
struct hlist_node *node;
struct hlist_node *last;
enum cpuhp_state cb_state;
@@ -76,6 +75,10 @@ static DEFINE_PER_CPU(struct cpuhp_cpu_state, cpuhp_state) = {
.fail = CPUHP_INVALID,
};
+#ifdef CONFIG_SMP
+cpumask_t cpus_booted_once_mask;
+#endif
+
#if defined(CONFIG_LOCKDEP) && defined(CONFIG_SMP)
static struct lockdep_map cpuhp_state_up_map =
STATIC_LOCKDEP_MAP_INIT("cpuhp_state-up", &cpuhp_state_up_map);
@@ -433,7 +436,7 @@ static inline bool cpu_smt_allowed(unsigned int cpu)
* CPU. Otherwise, a broadacasted MCE observing CR4.MCE=0b on any
* core will shutdown the machine.
*/
- return !per_cpu(cpuhp_state, cpu).booted_once;
+ return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}
#else
static inline bool cpu_smt_allowed(unsigned int cpu) { return true; }
@@ -1066,7 +1069,7 @@ void notify_cpu_starting(unsigned int cpu)
int ret;
rcu_cpu_starting(cpu); /* Enables RCU usage on this CPU. */
- st->booted_once = true;
+ cpumask_set_cpu(cpu, &cpus_booted_once_mask);
while (st->state < target) {
st->state++;
ret = cpuhp_invoke_callback(cpu, st->state, true, NULL, NULL);
@@ -2295,6 +2298,9 @@ EXPORT_SYMBOL(__cpu_present_mask);
struct cpumask __cpu_active_mask __read_mostly;
EXPORT_SYMBOL(__cpu_active_mask);
+atomic_t __num_online_cpus __read_mostly;
+EXPORT_SYMBOL(__num_online_cpus);
+
void init_cpu_present(const struct cpumask *src)
{
cpumask_copy(&__cpu_present_mask, src);
@@ -2310,6 +2316,27 @@ void init_cpu_online(const struct cpumask *src)
cpumask_copy(&__cpu_online_mask, src);
}
+void set_cpu_online(unsigned int cpu, bool online)
+{
+ /*
+ * atomic_inc/dec() is required to handle the horrid abuse of this
+ * function by the reboot and kexec code which invoke it from
+ * IPI/NMI broadcasts when shutting down CPUs. Invocation from
+ * regular CPU hotplug is properly serialized.
+ *
+ * Note, that the fact that __num_online_cpus is of type atomic_t
+ * does not protect readers which are not serialized against
+ * concurrent hotplug operations.
+ */
+ if (online) {
+ if (!cpumask_test_and_set_cpu(cpu, &__cpu_online_mask))
+ atomic_inc(&__num_online_cpus);
+ } else {
+ if (cpumask_test_and_clear_cpu(cpu, &__cpu_online_mask))
+ atomic_dec(&__num_online_cpus);
+ }
+}
+
/*
* Activate the first processor.
*/
@@ -2334,7 +2361,7 @@ void __init boot_cpu_init(void)
void __init boot_cpu_hotplug_init(void)
{
#ifdef CONFIG_SMP
- this_cpu_write(cpuhp_state.booted_once, true);
+ cpumask_set_cpu(smp_processor_id(), &cpus_booted_once_mask);
#endif
this_cpu_write(cpuhp_state.state, CPUHP_ONLINE);
}
diff --git a/lib/bitmap.c b/lib/bitmap.c
index bbe2589e8497..f9e834841e94 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -59,6 +59,26 @@ int __bitmap_equal(const unsigned long *bitmap1,
}
EXPORT_SYMBOL(__bitmap_equal);
+bool __bitmap_or_equal(const unsigned long *bitmap1,
+ const unsigned long *bitmap2,
+ const unsigned long *bitmap3,
+ unsigned int bits)
+{
+ unsigned int k, lim = bits / BITS_PER_LONG;
+ unsigned long tmp;
+
+ for (k = 0; k < lim; ++k) {
+ if ((bitmap1[k] | bitmap2[k]) != bitmap3[k])
+ return false;
+ }
+
+ if (!(bits % BITS_PER_LONG))
+ return true;
+
+ tmp = (bitmap1[k] | bitmap2[k]) ^ bitmap3[k];
+ return (tmp & BITMAP_LAST_WORD_MASK(bits)) == 0;
+}
+
void __bitmap_complement(unsigned long *dst, const unsigned long *src, unsigned int bits)
{
unsigned int k, lim = BITS_TO_LONGS(bits);
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