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-rw-r--r--arch/x86/kernel/acpi/cstate.c23
-rw-r--r--arch/x86/kernel/cpu/amd.c2
-rw-r--r--arch/x86/kernel/cpu/intel.c2
-rw-r--r--arch/x86/kernel/cpu/perf_event.c16
-rw-r--r--arch/x86/kernel/smpboot.c2
-rw-r--r--arch/x86/kernel/tsc.c318
6 files changed, 272 insertions, 91 deletions
diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
index d2b7f27781b..e69182fd01c 100644
--- a/arch/x86/kernel/acpi/cstate.c
+++ b/arch/x86/kernel/acpi/cstate.c
@@ -150,29 +150,6 @@ int acpi_processor_ffh_cstate_probe(unsigned int cpu,
}
EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_probe);
-/*
- * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
- * which can obviate IPI to trigger checking of need_resched.
- * We execute MONITOR against need_resched and enter optimized wait state
- * through MWAIT. Whenever someone changes need_resched, we would be woken
- * up from MWAIT (without an IPI).
- *
- * New with Core Duo processors, MWAIT can take some hints based on CPU
- * capability.
- */
-void mwait_idle_with_hints(unsigned long ax, unsigned long cx)
-{
- if (!need_resched()) {
- if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
- clflush((void *)&current_thread_info()->flags);
-
- __monitor((void *)&current_thread_info()->flags, 0, 0);
- smp_mb();
- if (!need_resched())
- __mwait(ax, cx);
- }
-}
-
void acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
{
unsigned int cpu = smp_processor_id();
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index bca023bdd6b..8bc79cddd9a 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -487,7 +487,7 @@ static void early_init_amd(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
if (!check_tsc_unstable())
- sched_clock_stable = 1;
+ set_sched_clock_stable();
}
#ifdef CONFIG_X86_64
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index ea04b342c02..1a439c047ff 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -93,7 +93,7 @@ static void early_init_intel(struct cpuinfo_x86 *c)
set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);
set_cpu_cap(c, X86_FEATURE_NONSTOP_TSC);
if (!check_tsc_unstable())
- sched_clock_stable = 1;
+ set_sched_clock_stable();
}
/* Penwell and Cloverview have the TSC which doesn't sleep on S3 */
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 8e132931614..b88645191fe 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -1883,21 +1883,27 @@ static struct pmu pmu = {
void arch_perf_update_userpage(struct perf_event_mmap_page *userpg, u64 now)
{
+ struct cyc2ns_data *data;
+
userpg->cap_user_time = 0;
userpg->cap_user_time_zero = 0;
userpg->cap_user_rdpmc = x86_pmu.attr_rdpmc;
userpg->pmc_width = x86_pmu.cntval_bits;
- if (!sched_clock_stable)
+ if (!sched_clock_stable())
return;
+ data = cyc2ns_read_begin();
+
userpg->cap_user_time = 1;
- userpg->time_mult = this_cpu_read(cyc2ns);
- userpg->time_shift = CYC2NS_SCALE_FACTOR;
- userpg->time_offset = this_cpu_read(cyc2ns_offset) - now;
+ userpg->time_mult = data->cyc2ns_mul;
+ userpg->time_shift = data->cyc2ns_shift;
+ userpg->time_offset = data->cyc2ns_offset - now;
userpg->cap_user_time_zero = 1;
- userpg->time_zero = this_cpu_read(cyc2ns_offset);
+ userpg->time_zero = data->cyc2ns_offset;
+
+ cyc2ns_read_end(data);
}
/*
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 85dc05a3aa0..f5252c4eec8 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -1417,7 +1417,9 @@ static inline void mwait_play_dead(void)
* The WBINVD is insufficient due to the spurious-wakeup
* case where we return around the loop.
*/
+ mb();
clflush(mwait_ptr);
+ mb();
__monitor(mwait_ptr, 0, 0);
mb();
__mwait(eax, 0);
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 930e5d48f56..6377fb28b95 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -11,6 +11,7 @@
#include <linux/clocksource.h>
#include <linux/percpu.h>
#include <linux/timex.h>
+#include <linux/static_key.h>
#include <asm/hpet.h>
#include <asm/timer.h>
@@ -37,13 +38,244 @@ static int __read_mostly tsc_unstable;
erroneous rdtsc usage on !cpu_has_tsc processors */
static int __read_mostly tsc_disabled = -1;
+static struct static_key __use_tsc = STATIC_KEY_INIT;
+
int tsc_clocksource_reliable;
+
+/*
+ * Use a ring-buffer like data structure, where a writer advances the head by
+ * writing a new data entry and a reader advances the tail when it observes a
+ * new entry.
+ *
+ * Writers are made to wait on readers until there's space to write a new
+ * entry.
+ *
+ * This means that we can always use an {offset, mul} pair to compute a ns
+ * value that is 'roughly' in the right direction, even if we're writing a new
+ * {offset, mul} pair during the clock read.
+ *
+ * The down-side is that we can no longer guarantee strict monotonicity anymore
+ * (assuming the TSC was that to begin with), because while we compute the
+ * intersection point of the two clock slopes and make sure the time is
+ * continuous at the point of switching; we can no longer guarantee a reader is
+ * strictly before or after the switch point.
+ *
+ * It does mean a reader no longer needs to disable IRQs in order to avoid
+ * CPU-Freq updates messing with his times, and similarly an NMI reader will
+ * no longer run the risk of hitting half-written state.
+ */
+
+struct cyc2ns {
+ struct cyc2ns_data data[2]; /* 0 + 2*24 = 48 */
+ struct cyc2ns_data *head; /* 48 + 8 = 56 */
+ struct cyc2ns_data *tail; /* 56 + 8 = 64 */
+}; /* exactly fits one cacheline */
+
+static DEFINE_PER_CPU_ALIGNED(struct cyc2ns, cyc2ns);
+
+struct cyc2ns_data *cyc2ns_read_begin(void)
+{
+ struct cyc2ns_data *head;
+
+ preempt_disable();
+
+ head = this_cpu_read(cyc2ns.head);
+ /*
+ * Ensure we observe the entry when we observe the pointer to it.
+ * matches the wmb from cyc2ns_write_end().
+ */
+ smp_read_barrier_depends();
+ head->__count++;
+ barrier();
+
+ return head;
+}
+
+void cyc2ns_read_end(struct cyc2ns_data *head)
+{
+ barrier();
+ /*
+ * If we're the outer most nested read; update the tail pointer
+ * when we're done. This notifies possible pending writers
+ * that we've observed the head pointer and that the other
+ * entry is now free.
+ */
+ if (!--head->__count) {
+ /*
+ * x86-TSO does not reorder writes with older reads;
+ * therefore once this write becomes visible to another
+ * cpu, we must be finished reading the cyc2ns_data.
+ *
+ * matches with cyc2ns_write_begin().
+ */
+ this_cpu_write(cyc2ns.tail, head);
+ }
+ preempt_enable();
+}
+
+/*
+ * Begin writing a new @data entry for @cpu.
+ *
+ * Assumes some sort of write side lock; currently 'provided' by the assumption
+ * that cpufreq will call its notifiers sequentially.
+ */
+static struct cyc2ns_data *cyc2ns_write_begin(int cpu)
+{
+ struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+ struct cyc2ns_data *data = c2n->data;
+
+ if (data == c2n->head)
+ data++;
+
+ /* XXX send an IPI to @cpu in order to guarantee a read? */
+
+ /*
+ * When we observe the tail write from cyc2ns_read_end(),
+ * the cpu must be done with that entry and its safe
+ * to start writing to it.
+ */
+ while (c2n->tail == data)
+ cpu_relax();
+
+ return data;
+}
+
+static void cyc2ns_write_end(int cpu, struct cyc2ns_data *data)
+{
+ struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+
+ /*
+ * Ensure the @data writes are visible before we publish the
+ * entry. Matches the data-depencency in cyc2ns_read_begin().
+ */
+ smp_wmb();
+
+ ACCESS_ONCE(c2n->head) = data;
+}
+
+/*
+ * Accelerators for sched_clock()
+ * convert from cycles(64bits) => nanoseconds (64bits)
+ * basic equation:
+ * ns = cycles / (freq / ns_per_sec)
+ * ns = cycles * (ns_per_sec / freq)
+ * ns = cycles * (10^9 / (cpu_khz * 10^3))
+ * ns = cycles * (10^6 / cpu_khz)
+ *
+ * Then we use scaling math (suggested by george@mvista.com) to get:
+ * ns = cycles * (10^6 * SC / cpu_khz) / SC
+ * ns = cycles * cyc2ns_scale / SC
+ *
+ * And since SC is a constant power of two, we can convert the div
+ * into a shift.
+ *
+ * We can use khz divisor instead of mhz to keep a better precision, since
+ * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
+ * (mathieu.desnoyers@polymtl.ca)
+ *
+ * -johnstul@us.ibm.com "math is hard, lets go shopping!"
+ */
+
+#define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
+
+static void cyc2ns_data_init(struct cyc2ns_data *data)
+{
+ data->cyc2ns_mul = 1U << CYC2NS_SCALE_FACTOR;
+ data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+ data->cyc2ns_offset = 0;
+ data->__count = 0;
+}
+
+static void cyc2ns_init(int cpu)
+{
+ struct cyc2ns *c2n = &per_cpu(cyc2ns, cpu);
+
+ cyc2ns_data_init(&c2n->data[0]);
+ cyc2ns_data_init(&c2n->data[1]);
+
+ c2n->head = c2n->data;
+ c2n->tail = c2n->data;
+}
+
+static inline unsigned long long cycles_2_ns(unsigned long long cyc)
+{
+ struct cyc2ns_data *data, *tail;
+ unsigned long long ns;
+
+ /*
+ * See cyc2ns_read_*() for details; replicated in order to avoid
+ * an extra few instructions that came with the abstraction.
+ * Notable, it allows us to only do the __count and tail update
+ * dance when its actually needed.
+ */
+
+ preempt_disable();
+ data = this_cpu_read(cyc2ns.head);
+ tail = this_cpu_read(cyc2ns.tail);
+
+ if (likely(data == tail)) {
+ ns = data->cyc2ns_offset;
+ ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+ } else {
+ data->__count++;
+
+ barrier();
+
+ ns = data->cyc2ns_offset;
+ ns += mul_u64_u32_shr(cyc, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+
+ barrier();
+
+ if (!--data->__count)
+ this_cpu_write(cyc2ns.tail, data);
+ }
+ preempt_enable();
+
+ return ns;
+}
+
+/* XXX surely we already have this someplace in the kernel?! */
+#define DIV_ROUND(n, d) (((n) + ((d) / 2)) / (d))
+
+static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
+{
+ unsigned long long tsc_now, ns_now;
+ struct cyc2ns_data *data;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ sched_clock_idle_sleep_event();
+
+ if (!cpu_khz)
+ goto done;
+
+ data = cyc2ns_write_begin(cpu);
+
+ rdtscll(tsc_now);
+ ns_now = cycles_2_ns(tsc_now);
+
+ /*
+ * Compute a new multiplier as per the above comment and ensure our
+ * time function is continuous; see the comment near struct
+ * cyc2ns_data.
+ */
+ data->cyc2ns_mul = DIV_ROUND(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR, cpu_khz);
+ data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
+ data->cyc2ns_offset = ns_now -
+ mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
+
+ cyc2ns_write_end(cpu, data);
+
+done:
+ sched_clock_idle_wakeup_event(0);
+ local_irq_restore(flags);
+}
/*
* Scheduler clock - returns current time in nanosec units.
*/
u64 native_sched_clock(void)
{
- u64 this_offset;
+ u64 tsc_now;
/*
* Fall back to jiffies if there's no TSC available:
@@ -53,16 +285,16 @@ u64 native_sched_clock(void)
* very important for it to be as fast as the platform
* can achieve it. )
*/
- if (unlikely(tsc_disabled)) {
+ if (!static_key_false(&__use_tsc)) {
/* No locking but a rare wrong value is not a big deal: */
return (jiffies_64 - INITIAL_JIFFIES) * (1000000000 / HZ);
}
/* read the Time Stamp Counter: */
- rdtscll(this_offset);
+ rdtscll(tsc_now);
/* return the value in ns */
- return __cycles_2_ns(this_offset);
+ return cycles_2_ns(tsc_now);
}
/* We need to define a real function for sched_clock, to override the
@@ -589,61 +821,11 @@ int recalibrate_cpu_khz(void)
EXPORT_SYMBOL(recalibrate_cpu_khz);
-/* Accelerators for sched_clock()
- * convert from cycles(64bits) => nanoseconds (64bits)
- * basic equation:
- * ns = cycles / (freq / ns_per_sec)
- * ns = cycles * (ns_per_sec / freq)
- * ns = cycles * (10^9 / (cpu_khz * 10^3))
- * ns = cycles * (10^6 / cpu_khz)
- *
- * Then we use scaling math (suggested by george@mvista.com) to get:
- * ns = cycles * (10^6 * SC / cpu_khz) / SC
- * ns = cycles * cyc2ns_scale / SC
- *
- * And since SC is a constant power of two, we can convert the div
- * into a shift.
- *
- * We can use khz divisor instead of mhz to keep a better precision, since
- * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
- * (mathieu.desnoyers@polymtl.ca)
- *
- * -johnstul@us.ibm.com "math is hard, lets go shopping!"
- */
-
-DEFINE_PER_CPU(unsigned long, cyc2ns);
-DEFINE_PER_CPU(unsigned long long, cyc2ns_offset);
-
-static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
-{
- unsigned long long tsc_now, ns_now, *offset;
- unsigned long flags, *scale;
-
- local_irq_save(flags);
- sched_clock_idle_sleep_event();
-
- scale = &per_cpu(cyc2ns, cpu);
- offset = &per_cpu(cyc2ns_offset, cpu);
-
- rdtscll(tsc_now);
- ns_now = __cycles_2_ns(tsc_now);
-
- if (cpu_khz) {
- *scale = ((NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR) +
- cpu_khz / 2) / cpu_khz;
- *offset = ns_now - mult_frac(tsc_now, *scale,
- (1UL << CYC2NS_SCALE_FACTOR));
- }
-
- sched_clock_idle_wakeup_event(0);
- local_irq_restore(flags);
-}
-
static unsigned long long cyc2ns_suspend;
void tsc_save_sched_clock_state(void)
{
- if (!sched_clock_stable)
+ if (!sched_clock_stable())
return;
cyc2ns_suspend = sched_clock();
@@ -663,16 +845,26 @@ void tsc_restore_sched_clock_state(void)
unsigned long flags;
int cpu;
- if (!sched_clock_stable)
+ if (!sched_clock_stable())
return;
local_irq_save(flags);
- __this_cpu_write(cyc2ns_offset, 0);
+ /*
+ * We're comming out of suspend, there's no concurrency yet; don't
+ * bother being nice about the RCU stuff, just write to both
+ * data fields.
+ */
+
+ this_cpu_write(cyc2ns.data[0].cyc2ns_offset, 0);
+ this_cpu_write(cyc2ns.data[1].cyc2ns_offset, 0);
+
offset = cyc2ns_suspend - sched_clock();
- for_each_possible_cpu(cpu)
- per_cpu(cyc2ns_offset, cpu) = offset;
+ for_each_possible_cpu(cpu) {
+ per_cpu(cyc2ns.data[0].cyc2ns_offset, cpu) = offset;
+ per_cpu(cyc2ns.data[1].cyc2ns_offset, cpu) = offset;
+ }
local_irq_restore(flags);
}
@@ -795,7 +987,7 @@ void mark_tsc_unstable(char *reason)
{
if (!tsc_unstable) {
tsc_unstable = 1;
- sched_clock_stable = 0;
+ clear_sched_clock_stable();
disable_sched_clock_irqtime();
pr_info("Marking TSC unstable due to %s\n", reason);
/* Change only the rating, when not registered */
@@ -995,14 +1187,18 @@ void __init tsc_init(void)
* speed as the bootup CPU. (cpufreq notifiers will fix this
* up if their speed diverges)
*/
- for_each_possible_cpu(cpu)
+ for_each_possible_cpu(cpu) {
+ cyc2ns_init(cpu);
set_cyc2ns_scale(cpu_khz, cpu);
+ }
if (tsc_disabled > 0)
return;
/* now allow native_sched_clock() to use rdtsc */
+
tsc_disabled = 0;
+ static_key_slow_inc(&__use_tsc);
if (!no_sched_irq_time)
enable_sched_clock_irqtime();
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2024-11-11 20:26:20 +0000