[patch] x86: unify/rewrite SMP TSC sync code

From: Ingo Molnar
Date: Fri Nov 24 2006 - 12:05:19 EST


Andrew,

could we try this one in -mm? It unifies (and simplifies) the TSC sync
code between i386 and x86_64, and also offers a stronger guarantee that
we'll only activate the TSC clock on CPU where the TSC is synced
correctly by the hardware.

Ingo

---------------->
From: Ingo Molnar <mingo@xxxxxxx>
[patch] x86: unify/rewrite SMP TSC sync code

make the TSC synchronization code more robust, and unify it between
x86_64 and i386.

The biggest change is the removal of the 'fix up TSCs' code on x86_64
and i386, in some rare cases it was /causing/ time-warps on SMP systems.

The new code only checks for TSC asynchronity - and if it can prove a
time-warp (if it can observe the TSC going backwards when going from one
CPU to another within a critical section), then the TSC clock-source is
turned off.

The TSC synchronization-checking code also got moved into a separate
file.

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
arch/i386/kernel/Makefile | 2
arch/i386/kernel/smpboot.c | 178 ++------------------------------
arch/i386/kernel/tsc.c | 4
arch/i386/kernel/tsc_sync.c | 1
arch/x86_64/kernel/Makefile | 2
arch/x86_64/kernel/smpboot.c | 230 ++----------------------------------------
arch/x86_64/kernel/time.c | 11 ++
arch/x86_64/kernel/tsc_sync.c | 187 ++++++++++++++++++++++++++++++++++
include/asm-i386/tsc.h | 49 --------
include/asm-x86_64/proto.h | 2
include/asm-x86_64/timex.h | 26 ----
include/asm-x86_64/tsc.h | 66 ++++++++++++
12 files changed, 295 insertions(+), 463 deletions(-)

Index: linux/arch/i386/kernel/Makefile
===================================================================
--- linux.orig/arch/i386/kernel/Makefile
+++ linux/arch/i386/kernel/Makefile
@@ -18,7 +18,7 @@ obj-$(CONFIG_X86_MSR) += msr.o
obj-$(CONFIG_X86_CPUID) += cpuid.o
obj-$(CONFIG_MICROCODE) += microcode.o
obj-$(CONFIG_APM) += apm.o
-obj-$(CONFIG_X86_SMP) += smp.o smpboot.o
+obj-$(CONFIG_X86_SMP) += smp.o smpboot.o tsc_sync.o
obj-$(CONFIG_X86_TRAMPOLINE) += trampoline.o
obj-$(CONFIG_X86_MPPARSE) += mpparse.o
obj-$(CONFIG_X86_LOCAL_APIC) += apic.o nmi.o
Index: linux/arch/i386/kernel/smpboot.c
===================================================================
--- linux.orig/arch/i386/kernel/smpboot.c
+++ linux/arch/i386/kernel/smpboot.c
@@ -88,12 +88,6 @@ cpumask_t cpu_possible_map;
EXPORT_SYMBOL(cpu_possible_map);
static cpumask_t smp_commenced_mask;

-/* TSC's upper 32 bits can't be written in eariler CPU (before prescott), there
- * is no way to resync one AP against BP. TBD: for prescott and above, we
- * should use IA64's algorithm
- */
-static int __devinitdata tsc_sync_disabled;
-
/* Per CPU bogomips and other parameters */
struct cpuinfo_x86 cpu_data[NR_CPUS] __cacheline_aligned;
EXPORT_SYMBOL(cpu_data);
@@ -210,151 +204,6 @@ valid_k7:
;
}

-/*
- * TSC synchronization.
- *
- * We first check whether all CPUs have their TSC's synchronized,
- * then we print a warning if not, and always resync.
- */
-
-static struct {
- atomic_t start_flag;
- atomic_t count_start;
- atomic_t count_stop;
- unsigned long long values[NR_CPUS];
-} tsc __initdata = {
- .start_flag = ATOMIC_INIT(0),
- .count_start = ATOMIC_INIT(0),
- .count_stop = ATOMIC_INIT(0),
-};
-
-#define NR_LOOPS 5
-
-static void __init synchronize_tsc_bp(void)
-{
- int i;
- unsigned long long t0;
- unsigned long long sum, avg;
- long long delta;
- unsigned int one_usec;
- int buggy = 0;
-
- printk(KERN_INFO "checking TSC synchronization across %u CPUs: ", num_booting_cpus());
-
- /* convert from kcyc/sec to cyc/usec */
- one_usec = cpu_khz / 1000;
-
- atomic_set(&tsc.start_flag, 1);
- wmb();
-
- /*
- * We loop a few times to get a primed instruction cache,
- * then the last pass is more or less synchronized and
- * the BP and APs set their cycle counters to zero all at
- * once. This reduces the chance of having random offsets
- * between the processors, and guarantees that the maximum
- * delay between the cycle counters is never bigger than
- * the latency of information-passing (cachelines) between
- * two CPUs.
- */
- for (i = 0; i < NR_LOOPS; i++) {
- /*
- * all APs synchronize but they loop on '== num_cpus'
- */
- while (atomic_read(&tsc.count_start) != num_booting_cpus()-1)
- cpu_relax();
- atomic_set(&tsc.count_stop, 0);
- wmb();
- /*
- * this lets the APs save their current TSC:
- */
- atomic_inc(&tsc.count_start);
-
- rdtscll(tsc.values[smp_processor_id()]);
- /*
- * We clear the TSC in the last loop:
- */
- if (i == NR_LOOPS-1)
- write_tsc(0, 0);
-
- /*
- * Wait for all APs to leave the synchronization point:
- */
- while (atomic_read(&tsc.count_stop) != num_booting_cpus()-1)
- cpu_relax();
- atomic_set(&tsc.count_start, 0);
- wmb();
- atomic_inc(&tsc.count_stop);
- }
-
- sum = 0;
- for (i = 0; i < NR_CPUS; i++) {
- if (cpu_isset(i, cpu_callout_map)) {
- t0 = tsc.values[i];
- sum += t0;
- }
- }
- avg = sum;
- do_div(avg, num_booting_cpus());
-
- for (i = 0; i < NR_CPUS; i++) {
- if (!cpu_isset(i, cpu_callout_map))
- continue;
- delta = tsc.values[i] - avg;
- if (delta < 0)
- delta = -delta;
- /*
- * We report bigger than 2 microseconds clock differences.
- */
- if (delta > 2*one_usec) {
- long long realdelta;
-
- if (!buggy) {
- buggy = 1;
- printk("\n");
- }
- realdelta = delta;
- do_div(realdelta, one_usec);
- if (tsc.values[i] < avg)
- realdelta = -realdelta;
-
- if (realdelta)
- printk(KERN_INFO "CPU#%d had %Ld usecs TSC "
- "skew, fixed it up.\n", i, realdelta);
- }
- }
- if (!buggy)
- printk("passed.\n");
-}
-
-static void __init synchronize_tsc_ap(void)
-{
- int i;
-
- /*
- * Not every cpu is online at the time
- * this gets called, so we first wait for the BP to
- * finish SMP initialization:
- */
- while (!atomic_read(&tsc.start_flag))
- cpu_relax();
-
- for (i = 0; i < NR_LOOPS; i++) {
- atomic_inc(&tsc.count_start);
- while (atomic_read(&tsc.count_start) != num_booting_cpus())
- cpu_relax();
-
- rdtscll(tsc.values[smp_processor_id()]);
- if (i == NR_LOOPS-1)
- write_tsc(0, 0);
-
- atomic_inc(&tsc.count_stop);
- while (atomic_read(&tsc.count_stop) != num_booting_cpus())
- cpu_relax();
- }
-}
-#undef NR_LOOPS
-
extern void calibrate_delay(void);

static atomic_t init_deasserted;
@@ -440,12 +289,6 @@ static void __devinit smp_callin(void)
* Allow the master to continue.
*/
cpu_set(cpuid, cpu_callin_map);
-
- /*
- * Synchronize the TSC with the BP
- */
- if (cpu_has_tsc && cpu_khz && !tsc_sync_disabled)
- synchronize_tsc_ap();
}

static int cpucount;
@@ -545,6 +388,11 @@ static void __devinit start_secondary(vo
smp_callin();
while (!cpu_isset(smp_processor_id(), smp_commenced_mask))
rep_nop();
+ /*
+ * Check TSC synchronization with the BP:
+ */
+ check_tsc_sync_target();
+
setup_secondary_APIC_clock();
if (nmi_watchdog == NMI_IO_APIC) {
disable_8259A_irq(0);
@@ -1091,8 +939,6 @@ static int __cpuinit __smp_prepare_cpu(i
info.cpu = cpu;
INIT_WORK(&task, do_warm_boot_cpu, &info);

- tsc_sync_disabled = 1;
-
/* init low mem mapping */
clone_pgd_range(swapper_pg_dir, swapper_pg_dir + USER_PGD_PTRS,
KERNEL_PGD_PTRS);
@@ -1100,7 +946,6 @@ static int __cpuinit __smp_prepare_cpu(i
schedule_work(&task);
wait_for_completion(&done);

- tsc_sync_disabled = 0;
zap_low_mappings();
ret = 0;
exit:
@@ -1316,12 +1161,6 @@ static void __init smp_boot_cpus(unsigne
smpboot_setup_io_apic();

setup_boot_APIC_clock();
-
- /*
- * Synchronize the TSC with the AP
- */
- if (cpu_has_tsc && cpucount && cpu_khz)
- synchronize_tsc_bp();
}

/* These are wrappers to interface to the new boot process. Someone
@@ -1456,9 +1295,16 @@ int __devinit __cpu_up(unsigned int cpu)
}

local_irq_enable();
+
per_cpu(cpu_state, cpu) = CPU_UP_PREPARE;
/* Unleash the CPU! */
cpu_set(cpu, smp_commenced_mask);
+
+ /*
+ * Check TSC synchronization with the AP:
+ */
+ check_tsc_sync_source(cpu);
+
while (!cpu_isset(cpu, cpu_online_map))
cpu_relax();
return 0;
Index: linux/arch/i386/kernel/tsc.c
===================================================================
--- linux.orig/arch/i386/kernel/tsc.c
+++ linux/arch/i386/kernel/tsc.c
@@ -434,8 +434,10 @@ out:
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
-static __init int unsynchronized_tsc(void)
+__init int unsynchronized_tsc(void)
{
+ if (!cpu_has_tsc || tsc_unstable)
+ return 1;
/*
* Intel systems are normally all synchronized.
* Exceptions must mark TSC as unstable:
Index: linux/arch/i386/kernel/tsc_sync.c
===================================================================
--- /dev/null
+++ linux/arch/i386/kernel/tsc_sync.c
@@ -0,0 +1 @@
+#include "../../x86_64/kernel/tsc_sync.c"
Index: linux/arch/x86_64/kernel/Makefile
===================================================================
--- linux.orig/arch/x86_64/kernel/Makefile
+++ linux/arch/x86_64/kernel/Makefile
@@ -19,7 +19,7 @@ obj-$(CONFIG_ACPI) += acpi/
obj-$(CONFIG_X86_MSR) += msr.o
obj-$(CONFIG_MICROCODE) += microcode.o
obj-$(CONFIG_X86_CPUID) += cpuid.o
-obj-$(CONFIG_SMP) += smp.o smpboot.o trampoline.o
+obj-$(CONFIG_SMP) += smp.o smpboot.o trampoline.o tsc_sync.o
obj-y += apic.o nmi.o
obj-y += io_apic.o mpparse.o \
genapic.o genapic_cluster.o genapic_flat.o
Index: linux/arch/x86_64/kernel/smpboot.c
===================================================================
--- linux.orig/arch/x86_64/kernel/smpboot.c
+++ linux/arch/x86_64/kernel/smpboot.c
@@ -147,217 +147,6 @@ static void __cpuinit smp_store_cpu_info
print_cpu_info(c);
}

-/*
- * New Funky TSC sync algorithm borrowed from IA64.
- * Main advantage is that it doesn't reset the TSCs fully and
- * in general looks more robust and it works better than my earlier
- * attempts. I believe it was written by David Mosberger. Some minor
- * adjustments for x86-64 by me -AK
- *
- * Original comment reproduced below.
- *
- * Synchronize TSC of the current (slave) CPU with the TSC of the
- * MASTER CPU (normally the time-keeper CPU). We use a closed loop to
- * eliminate the possibility of unaccounted-for errors (such as
- * getting a machine check in the middle of a calibration step). The
- * basic idea is for the slave to ask the master what itc value it has
- * and to read its own itc before and after the master responds. Each
- * iteration gives us three timestamps:
- *
- * slave master
- *
- * t0 ---\
- * ---\
- * --->
- * tm
- * /---
- * /---
- * t1 <---
- *
- *
- * The goal is to adjust the slave's TSC such that tm falls exactly
- * half-way between t0 and t1. If we achieve this, the clocks are
- * synchronized provided the interconnect between the slave and the
- * master is symmetric. Even if the interconnect were asymmetric, we
- * would still know that the synchronization error is smaller than the
- * roundtrip latency (t0 - t1).
- *
- * When the interconnect is quiet and symmetric, this lets us
- * synchronize the TSC to within one or two cycles. However, we can
- * only *guarantee* that the synchronization is accurate to within a
- * round-trip time, which is typically in the range of several hundred
- * cycles (e.g., ~500 cycles). In practice, this means that the TSCs
- * are usually almost perfectly synchronized, but we shouldn't assume
- * that the accuracy is much better than half a micro second or so.
- *
- * [there are other errors like the latency of RDTSC and of the
- * WRMSR. These can also account to hundreds of cycles. So it's
- * probably worse. It claims 153 cycles error on a dual Opteron,
- * but I suspect the numbers are actually somewhat worse -AK]
- */
-
-#define MASTER 0
-#define SLAVE (SMP_CACHE_BYTES/8)
-
-/* Intentionally don't use cpu_relax() while TSC synchronization
- because we don't want to go into funky power save modi or cause
- hypervisors to schedule us away. Going to sleep would likely affect
- latency and low latency is the primary objective here. -AK */
-#define no_cpu_relax() barrier()
-
-static __cpuinitdata DEFINE_SPINLOCK(tsc_sync_lock);
-static volatile __cpuinitdata unsigned long go[SLAVE + 1];
-static int notscsync __cpuinitdata;
-
-#undef DEBUG_TSC_SYNC
-
-#define NUM_ROUNDS 64 /* magic value */
-#define NUM_ITERS 5 /* likewise */
-
-/* Callback on boot CPU */
-static __cpuinit void sync_master(void *arg)
-{
- unsigned long flags, i;
-
- go[MASTER] = 0;
-
- local_irq_save(flags);
- {
- for (i = 0; i < NUM_ROUNDS*NUM_ITERS; ++i) {
- while (!go[MASTER])
- no_cpu_relax();
- go[MASTER] = 0;
- rdtscll(go[SLAVE]);
- }
- }
- local_irq_restore(flags);
-}
-
-/*
- * Return the number of cycles by which our tsc differs from the tsc
- * on the master (time-keeper) CPU. A positive number indicates our
- * tsc is ahead of the master, negative that it is behind.
- */
-static inline long
-get_delta(long *rt, long *master)
-{
- unsigned long best_t0 = 0, best_t1 = ~0UL, best_tm = 0;
- unsigned long tcenter, t0, t1, tm;
- int i;
-
- for (i = 0; i < NUM_ITERS; ++i) {
- rdtscll(t0);
- go[MASTER] = 1;
- while (!(tm = go[SLAVE]))
- no_cpu_relax();
- go[SLAVE] = 0;
- rdtscll(t1);
-
- if (t1 - t0 < best_t1 - best_t0)
- best_t0 = t0, best_t1 = t1, best_tm = tm;
- }
-
- *rt = best_t1 - best_t0;
- *master = best_tm - best_t0;
-
- /* average best_t0 and best_t1 without overflow: */
- tcenter = (best_t0/2 + best_t1/2);
- if (best_t0 % 2 + best_t1 % 2 == 2)
- ++tcenter;
- return tcenter - best_tm;
-}
-
-static __cpuinit void sync_tsc(unsigned int master)
-{
- int i, done = 0;
- long delta, adj, adjust_latency = 0;
- unsigned long flags, rt, master_time_stamp, bound;
-#ifdef DEBUG_TSC_SYNC
- static struct syncdebug {
- long rt; /* roundtrip time */
- long master; /* master's timestamp */
- long diff; /* difference between midpoint and master's timestamp */
- long lat; /* estimate of tsc adjustment latency */
- } t[NUM_ROUNDS] __cpuinitdata;
-#endif
-
- printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n",
- smp_processor_id(), master);
-
- go[MASTER] = 1;
-
- /* It is dangerous to broadcast IPI as cpus are coming up,
- * as they may not be ready to accept them. So since
- * we only need to send the ipi to the boot cpu direct
- * the message, and avoid the race.
- */
- smp_call_function_single(master, sync_master, NULL, 1, 0);
-
- while (go[MASTER]) /* wait for master to be ready */
- no_cpu_relax();
-
- spin_lock_irqsave(&tsc_sync_lock, flags);
- {
- for (i = 0; i < NUM_ROUNDS; ++i) {
- delta = get_delta(&rt, &master_time_stamp);
- if (delta == 0) {
- done = 1; /* let's lock on to this... */
- bound = rt;
- }
-
- if (!done) {
- unsigned long t;
- if (i > 0) {
- adjust_latency += -delta;
- adj = -delta + adjust_latency/4;
- } else
- adj = -delta;
-
- rdtscll(t);
- wrmsrl(MSR_IA32_TSC, t + adj);
- }
-#ifdef DEBUG_TSC_SYNC
- t[i].rt = rt;
- t[i].master = master_time_stamp;
- t[i].diff = delta;
- t[i].lat = adjust_latency/4;
-#endif
- }
- }
- spin_unlock_irqrestore(&tsc_sync_lock, flags);
-
-#ifdef DEBUG_TSC_SYNC
- for (i = 0; i < NUM_ROUNDS; ++i)
- printk("rt=%5ld master=%5ld diff=%5ld adjlat=%5ld\n",
- t[i].rt, t[i].master, t[i].diff, t[i].lat);
-#endif
-
- printk(KERN_INFO
- "CPU %d: synchronized TSC with CPU %u (last diff %ld cycles, "
- "maxerr %lu cycles)\n",
- smp_processor_id(), master, delta, rt);
-}
-
-static void __cpuinit tsc_sync_wait(void)
-{
- /*
- * When the CPU has synchronized TSCs assume the BIOS
- * or the hardware already synced. Otherwise we could
- * mess up a possible perfect synchronization with a
- * not-quite-perfect algorithm.
- */
- if (notscsync || !cpu_has_tsc || !unsynchronized_tsc())
- return;
- sync_tsc(0);
-}
-
-static __init int notscsync_setup(char *s)
-{
- notscsync = 1;
- return 1;
-}
-__setup("notscsync", notscsync_setup);
-
static atomic_t init_deasserted __cpuinitdata;

/*
@@ -545,6 +334,11 @@ void __cpuinit start_secondary(void)
/* otherwise gcc will move up the smp_processor_id before the cpu_init */
barrier();

+ /*
+ * Check TSC sync first:
+ */
+ check_tsc_sync_target();
+
Dprintk("cpu %d: setting up apic clock\n", smp_processor_id());
setup_secondary_APIC_clock();

@@ -564,14 +358,6 @@ void __cpuinit start_secondary(void)
*/
set_cpu_sibling_map(smp_processor_id());

- /*
- * Wait for TSC sync to not schedule things before.
- * We still process interrupts, which could see an inconsistent
- * time in that window unfortunately.
- * Do this here because TSC sync has global unprotected state.
- */
- tsc_sync_wait();
-
/*
* We need to hold call_lock, so there is no inconsistency
* between the time smp_call_function() determines number of
@@ -591,6 +377,7 @@ void __cpuinit start_secondary(void)
cpu_set(smp_processor_id(), cpu_online_map);
per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
spin_unlock(&vector_lock);
+
unlock_ipi_call_lock();

cpu_idle();
@@ -1165,6 +952,11 @@ int __cpuinit __cpu_up(unsigned int cpu)
/* Unleash the CPU! */
Dprintk("waiting for cpu %d\n", cpu);

+ /*
+ * Make sure and check TSC sync:
+ */
+ check_tsc_sync_source(cpu);
+
while (!cpu_isset(cpu, cpu_online_map))
cpu_relax();
err = 0;
Index: linux/arch/x86_64/kernel/time.c
===================================================================
--- linux.orig/arch/x86_64/kernel/time.c
+++ linux/arch/x86_64/kernel/time.c
@@ -922,12 +922,23 @@ void __init time_init(void)
#endif
}

+static int tsc_unstable = 0;
+
+void mark_tsc_unstable(void)
+{
+ tsc_unstable = 1;
+}
+EXPORT_SYMBOL_GPL(mark_tsc_unstable);
+
/*
* Make an educated guess if the TSC is trustworthy and synchronized
* over all CPUs.
*/
__cpuinit int unsynchronized_tsc(void)
{
+ if (tsc_unstable)
+ return 1;
+
#ifdef CONFIG_SMP
if (apic_is_clustered_box())
return 1;
Index: linux/arch/x86_64/kernel/tsc_sync.c
===================================================================
--- /dev/null
+++ linux/arch/x86_64/kernel/tsc_sync.c
@@ -0,0 +1,187 @@
+/*
+ * arch/i386/kernel/tsc_sync.c: check TSC synchronization.
+ *
+ * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar
+ *
+ * We check whether all boot CPUs have their TSC's synchronized,
+ * print a warning if not and turn off the TSC clock-source.
+ *
+ * The warp-check is point-to-point between two CPUs, the CPU
+ * initiating the bootup is the 'source CPU', the freshly booting
+ * CPU is the 'target CPU'.
+ *
+ * Only two CPUs may participate - they can enter in any order.
+ * ( The serial nature of the boot logic and the CPU hotplug lock
+ * protects against more than 2 CPUs entering this code. )
+ */
+#include <linux/spinlock.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+#include <linux/nmi.h>
+#include <asm/tsc.h>
+
+/*
+ * Entry/exit counters that make sure that both CPUs
+ * run the measurement code at once:
+ */
+static __cpuinitdata atomic_t start_count;
+static __cpuinitdata atomic_t stop_count;
+
+/*
+ * We use a raw spinlock in this exceptional case, because
+ * we want to have the fastest, inlined, non-debug version
+ * of a critical section, to be able to prove TSC time-warps:
+ */
+static __cpuinitdata raw_spinlock_t sync_lock = __RAW_SPIN_LOCK_UNLOCKED;
+static __cpuinitdata cycles_t last_tsc;
+static __cpuinitdata cycles_t max_warp;
+static __cpuinitdata int nr_warps;
+
+/*
+ * TSC-warp measurement loop running on both CPUs:
+ */
+static __cpuinit void check_tsc_warp(void)
+{
+ cycles_t start, now, prev, end;
+ int i;
+
+ start = get_cycles_sync();
+ /*
+ * The measurement runs for 20 msecs:
+ */
+ end = start + cpu_khz * 20ULL;
+ now = start;
+
+ for (i = 0; ; i++) {
+ /*
+ * We take the global lock, measure TSC, save the
+ * previous TSC that was measured (possibly on
+ * another CPU) and update the previous TSC timestamp.
+ */
+ __raw_spin_lock(&sync_lock);
+ prev = last_tsc;
+ now = get_cycles_sync();
+ last_tsc = now;
+ __raw_spin_unlock(&sync_lock);
+
+ /*
+ * Be nice every now and then (and also check whether
+ * measurement is done [we also insert a 100 million
+ * loops safety exit, so we dont lock up in case the
+ * TSC readout is totally broken]):
+ */
+ if (unlikely(!(i & 7))) {
+ if (now > end || i > 100000000)
+ break;
+ cpu_relax();
+ touch_nmi_watchdog();
+ }
+ /*
+ * Outside the critical section we can now see whether
+ * we saw a time-warp of the TSC going backwards:
+ */
+ if (unlikely(prev > now)) {
+ __raw_spin_lock(&sync_lock);
+ max_warp = max(max_warp, prev - now);
+ nr_warps++;
+ __raw_spin_unlock(&sync_lock);
+ }
+
+ }
+}
+
+/*
+ * Source CPU calls into this - it waits for the freshly booted
+ * target CPU to arrive and then starts the measurement:
+ */
+void __cpuinit check_tsc_sync_source(int cpu)
+{
+ int cpus = 2;
+
+ /*
+ * No need to check if we already know that the TSC is not
+ * synchronized:
+ */
+ if (unsynchronized_tsc())
+ return;
+
+ printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:",
+ smp_processor_id(), cpu);
+
+ /*
+ * Reset it - in case this is a second bootup:
+ */
+ atomic_set(&stop_count, 0);
+
+ /*
+ * Wait for the target to arrive:
+ */
+ while (atomic_read(&start_count) != cpus-1)
+ cpu_relax();
+ /*
+ * Trigger the target to continue into the measurement too:
+ */
+ atomic_inc(&start_count);
+
+ check_tsc_warp();
+
+ while (atomic_read(&stop_count) != cpus-1)
+ cpu_relax();
+
+ /*
+ * Reset it - just in case we boot another CPU later:
+ */
+ atomic_set(&start_count, 0);
+
+ if (nr_warps) {
+ printk("\n");
+ printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
+ " turning off TSC clock.\n", max_warp);
+ mark_tsc_unstable();
+ nr_warps = 0;
+ max_warp = 0;
+ last_tsc = 0;
+ } else {
+ printk(" passed.\n");
+ }
+
+ /*
+ * Let the target continue with the bootup:
+ */
+ atomic_inc(&stop_count);
+}
+
+/*
+ * Freshly booted CPUs call into this:
+ */
+void __cpuinit check_tsc_sync_target(void)
+{
+ int cpus = 2;
+
+ if (unsynchronized_tsc())
+ return;
+
+ /*
+ * Register this CPU's participation and wait for the
+ * source CPU to start the measurement:
+ */
+ atomic_inc(&start_count);
+ while (atomic_read(&start_count) != cpus)
+ cpu_relax();
+
+ check_tsc_warp();
+
+ /*
+ * Ok, we are done:
+ */
+ atomic_inc(&stop_count);
+
+ /*
+ * Wait for the source CPU to print stuff:
+ */
+ while (atomic_read(&stop_count) != cpus)
+ cpu_relax();
+}
+#undef NR_LOOPS
+
Index: linux/include/asm-i386/tsc.h
===================================================================
--- linux.orig/include/asm-i386/tsc.h
+++ linux/include/asm-i386/tsc.h
@@ -1,48 +1 @@
-/*
- * linux/include/asm-i386/tsc.h
- *
- * i386 TSC related functions
- */
-#ifndef _ASM_i386_TSC_H
-#define _ASM_i386_TSC_H
-
-#include <asm/processor.h>
-
-/*
- * Standard way to access the cycle counter on i586+ CPUs.
- * Currently only used on SMP.
- *
- * If you really have a SMP machine with i486 chips or older,
- * compile for that, and this will just always return zero.
- * That's ok, it just means that the nicer scheduling heuristics
- * won't work for you.
- *
- * We only use the low 32 bits, and we'd simply better make sure
- * that we reschedule before that wraps. Scheduling at least every
- * four billion cycles just basically sounds like a good idea,
- * regardless of how fast the machine is.
- */
-typedef unsigned long long cycles_t;
-
-extern unsigned int cpu_khz;
-extern unsigned int tsc_khz;
-
-static inline cycles_t get_cycles(void)
-{
- unsigned long long ret = 0;
-
-#ifndef CONFIG_X86_TSC
- if (!cpu_has_tsc)
- return 0;
-#endif
-
-#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
- rdtscll(ret);
-#endif
- return ret;
-}
-
-extern void tsc_init(void);
-extern void mark_tsc_unstable(void);
-
-#endif
+#include <asm-x86_64/tsc.h>
Index: linux/include/asm-x86_64/proto.h
===================================================================
--- linux.orig/include/asm-x86_64/proto.h
+++ linux/include/asm-x86_64/proto.h
@@ -92,8 +92,6 @@ extern void check_efer(void);

extern int unhandled_signal(struct task_struct *tsk, int sig);

-extern int unsynchronized_tsc(void);
-
extern void select_idle_routine(const struct cpuinfo_x86 *c);

extern unsigned long table_start, table_end;
Index: linux/include/asm-x86_64/timex.h
===================================================================
--- linux.orig/include/asm-x86_64/timex.h
+++ linux/include/asm-x86_64/timex.h
@@ -12,35 +12,11 @@
#include <asm/hpet.h>
#include <asm/system.h>
#include <asm/processor.h>
+#include <asm/tsc.h>
#include <linux/compiler.h>

#define CLOCK_TICK_RATE PIT_TICK_RATE /* Underlying HZ */

-typedef unsigned long long cycles_t;
-
-static inline cycles_t get_cycles (void)
-{
- unsigned long long ret;
-
- rdtscll(ret);
- return ret;
-}
-
-/* Like get_cycles, but make sure the CPU is synchronized. */
-static __always_inline cycles_t get_cycles_sync(void)
-{
- unsigned long long ret;
- unsigned eax;
- /* Don't do an additional sync on CPUs where we know
- RDTSC is already synchronous. */
- alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
- "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
- rdtscll(ret);
- return ret;
-}
-
-extern unsigned int cpu_khz;
-
extern int read_current_timer(unsigned long *timer_value);
#define ARCH_HAS_READ_CURRENT_TIMER 1

Index: linux/include/asm-x86_64/tsc.h
===================================================================
--- /dev/null
+++ linux/include/asm-x86_64/tsc.h
@@ -0,0 +1,66 @@
+/*
+ * linux/include/asm-x86_64/tsc.h
+ *
+ * x86_64 TSC related functions
+ */
+#ifndef _ASM_x86_64_TSC_H
+#define _ASM_x86_64_TSC_H
+
+#include <asm/processor.h>
+
+/*
+ * Standard way to access the cycle counter.
+ */
+typedef unsigned long long cycles_t;
+
+extern unsigned int cpu_khz;
+extern unsigned int tsc_khz;
+
+static inline cycles_t get_cycles(void)
+{
+ unsigned long long ret = 0;
+
+#ifndef CONFIG_X86_TSC
+ if (!cpu_has_tsc)
+ return 0;
+#endif
+
+#if defined(CONFIG_X86_GENERIC) || defined(CONFIG_X86_TSC)
+ rdtscll(ret);
+#endif
+ return ret;
+}
+
+/* Like get_cycles, but make sure the CPU is synchronized. */
+static __always_inline cycles_t get_cycles_sync(void)
+{
+ unsigned long long ret;
+#ifdef X86_FEATURE_SYNC_RDTSC
+ unsigned eax;
+
+ /*
+ * Don't do an additional sync on CPUs where we know
+ * RDTSC is already synchronous:
+ */
+ alternative_io("cpuid", ASM_NOP2, X86_FEATURE_SYNC_RDTSC,
+ "=a" (eax), "0" (1) : "ebx","ecx","edx","memory");
+#else
+ sync_core();
+#endif
+ rdtscll(ret);
+
+ return ret;
+}
+
+extern void tsc_init(void);
+extern void mark_tsc_unstable(void);
+extern int unsynchronized_tsc(void);
+
+/*
+ * Boot-time check whether the TSCs are synchronized across
+ * all CPUs/cores:
+ */
+extern void check_tsc_sync_source(int cpu);
+extern void check_tsc_sync_target(void);
+
+#endif
-
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