Merge branch 'x86-timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel...

Pull x86 timer updates from Ingo Molnar:
 "This tree includes a HPET overhead micro-optimization plus new TSC
  frequencies for newer Intel CPUs"

* 'x86-timers-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/tsc: Add additional Intel CPU models to the crystal quirk list
  x86/tsc: Use cpu id defines instead of hex constants
  x86/hpet: Reduce HPET counter read contention

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index c6dfd80..274fab9 100644 (file)
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -756,10 +756,104 @@ static void hpet_reserve_msi_timers(struct hpet_data *hd)
 /*
  * Clock source related code
  */
+#if defined(CONFIG_SMP) && defined(CONFIG_64BIT)
+/*
+ * Reading the HPET counter is a very slow operation. If a large number of
+ * CPUs are trying to access the HPET counter simultaneously, it can cause
+ * massive delay and slow down system performance dramatically. This may
+ * happen when HPET is the default clock source instead of TSC. For a
+ * really large system with hundreds of CPUs, the slowdown may be so
+ * severe that it may actually crash the system because of a NMI watchdog
+ * soft lockup, for example.
+ *
+ * If multiple CPUs are trying to access the HPET counter at the same time,
+ * we don't actually need to read the counter multiple times. Instead, the
+ * other CPUs can use the counter value read by the first CPU in the group.
+ *
+ * This special feature is only enabled on x86-64 systems. It is unlikely
+ * that 32-bit x86 systems will have enough CPUs to require this feature
+ * with its associated locking overhead. And we also need 64-bit atomic
+ * read.
+ *
+ * The lock and the hpet value are stored together and can be read in a
+ * single atomic 64-bit read. It is explicitly assumed that arch_spinlock_t
+ * is 32 bits in size.
+ */
+union hpet_lock {
+       struct {
+               arch_spinlock_t lock;
+               u32 value;
+       };
+       u64 lockval;
+};
+
+static union hpet_lock hpet __cacheline_aligned = {
+       { .lock = __ARCH_SPIN_LOCK_UNLOCKED, },
+};
+
+static cycle_t read_hpet(struct clocksource *cs)
+{
+       unsigned long flags;
+       union hpet_lock old, new;
+
+       BUILD_BUG_ON(sizeof(union hpet_lock) != 8);
+
+       /*
+        * Read HPET directly if in NMI.
+        */
+       if (in_nmi())
+               return (cycle_t)hpet_readl(HPET_COUNTER);
+
+       /*
+        * Read the current state of the lock and HPET value atomically.
+        */
+       old.lockval = READ_ONCE(hpet.lockval);
+
+       if (arch_spin_is_locked(&old.lock))
+               goto contended;
+
+       local_irq_save(flags);
+       if (arch_spin_trylock(&hpet.lock)) {
+               new.value = hpet_readl(HPET_COUNTER);
+               /*
+                * Use WRITE_ONCE() to prevent store tearing.
+                */
+               WRITE_ONCE(hpet.value, new.value);
+               arch_spin_unlock(&hpet.lock);
+               local_irq_restore(flags);
+               return (cycle_t)new.value;
+       }
+       local_irq_restore(flags);
+
+contended:
+       /*
+        * Contended case
+        * --------------
+        * Wait until the HPET value change or the lock is free to indicate
+        * its value is up-to-date.
+        *
+        * It is possible that old.value has already contained the latest
+        * HPET value while the lock holder was in the process of releasing
+        * the lock. Checking for lock state change will enable us to return
+        * the value immediately instead of waiting for the next HPET reader
+        * to come along.
+        */
+       do {
+               cpu_relax();
+               new.lockval = READ_ONCE(hpet.lockval);
+       } while ((new.value == old.value) && arch_spin_is_locked(&new.lock));
+
+       return (cycle_t)new.value;
+}
+#else
+/*
+ * For UP or 32-bit.
+ */
 static cycle_t read_hpet(struct clocksource *cs)
 {
        return (cycle_t)hpet_readl(HPET_COUNTER);
 }
+#endif
 
 static struct clocksource clocksource_hpet = {
        .name           = "hpet",

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 78b9cb5..46b2f41 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -23,6 +23,7 @@
 #include <asm/x86_init.h>
 #include <asm/geode.h>
 #include <asm/apic.h>
+#include <asm/intel-family.h>
 
 unsigned int __read_mostly cpu_khz;    /* TSC clocks / usec, not used here */
 EXPORT_SYMBOL(cpu_khz);
@@ -686,11 +687,16 @@ unsigned long native_calibrate_tsc(void)
 
        if (crystal_khz == 0) {
                switch (boot_cpu_data.x86_model) {
-               case 0x4E:      /* SKL */
-               case 0x5E:      /* SKL */
+               case INTEL_FAM6_SKYLAKE_MOBILE:
+               case INTEL_FAM6_SKYLAKE_DESKTOP:
+               case INTEL_FAM6_KABYLAKE_MOBILE:
+               case INTEL_FAM6_KABYLAKE_DESKTOP:
                        crystal_khz = 24000;    /* 24.0 MHz */
                        break;
-               case 0x5C:      /* BXT */
+               case INTEL_FAM6_SKYLAKE_X:
+                       crystal_khz = 25000;    /* 25.0 MHz */
+                       break;
+               case INTEL_FAM6_ATOM_GOLDMONT:
                        crystal_khz = 19200;    /* 19.2 MHz */
                        break;
                }