[PATCH] x86: 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@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index f46a4d0..6ddffe8 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/arch/i386/kernel/smpboot.c
@@ -94,12 +94,6 @@
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);
@@ -216,151 +210,6 @@
;
}
-/*
- * 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 __cpuinitdata = {
- .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 __cpuinit 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;
@@ -446,12 +295,6 @@
* 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;
@@ -554,6 +397,11 @@
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_clock();
if (nmi_watchdog == NMI_IO_APIC) {
disable_8259A_irq(0);
@@ -1125,8 +973,6 @@
info.cpu = cpu;
INIT_WORK(&info.task, do_warm_boot_cpu);
- tsc_sync_disabled = 1;
-
/* init low mem mapping */
clone_pgd_range(swapper_pg_dir, swapper_pg_dir + USER_PGD_PTRS,
min_t(unsigned long, KERNEL_PGD_PTRS, USER_PGD_PTRS));
@@ -1134,7 +980,6 @@
schedule_work(&info.task);
wait_for_completion(&done);
- tsc_sync_disabled = 0;
zap_low_mappings();
ret = 0;
exit:
@@ -1331,12 +1176,6 @@
smpboot_setup_io_apic();
setup_boot_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
@@ -1471,9 +1310,16 @@
}
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();