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authorAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-08-05 17:04:01 -0300
committerAndré Fabian Silva Delgado <emulatorman@parabola.nu>2015-08-05 17:04:01 -0300
commit57f0f512b273f60d52568b8c6b77e17f5636edc0 (patch)
tree5e910f0e82173f4ef4f51111366a3f1299037a7b /arch/x86/xen/spinlock.c
Initial import
Diffstat (limited to 'arch/x86/xen/spinlock.c')
-rw-r--r--arch/x86/xen/spinlock.c353
1 files changed, 353 insertions, 0 deletions
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
new file mode 100644
index 000000000..956374c1e
--- /dev/null
+++ b/arch/x86/xen/spinlock.c
@@ -0,0 +1,353 @@
+/*
+ * Split spinlock implementation out into its own file, so it can be
+ * compiled in a FTRACE-compatible way.
+ */
+#include <linux/kernel_stat.h>
+#include <linux/spinlock.h>
+#include <linux/debugfs.h>
+#include <linux/log2.h>
+#include <linux/gfp.h>
+#include <linux/slab.h>
+
+#include <asm/paravirt.h>
+
+#include <xen/interface/xen.h>
+#include <xen/events.h>
+
+#include "xen-ops.h"
+#include "debugfs.h"
+
+enum xen_contention_stat {
+ TAKEN_SLOW,
+ TAKEN_SLOW_PICKUP,
+ TAKEN_SLOW_SPURIOUS,
+ RELEASED_SLOW,
+ RELEASED_SLOW_KICKED,
+ NR_CONTENTION_STATS
+};
+
+
+#ifdef CONFIG_XEN_DEBUG_FS
+#define HISTO_BUCKETS 30
+static struct xen_spinlock_stats
+{
+ u32 contention_stats[NR_CONTENTION_STATS];
+ u32 histo_spin_blocked[HISTO_BUCKETS+1];
+ u64 time_blocked;
+} spinlock_stats;
+
+static u8 zero_stats;
+
+static inline void check_zero(void)
+{
+ u8 ret;
+ u8 old = READ_ONCE(zero_stats);
+ if (unlikely(old)) {
+ ret = cmpxchg(&zero_stats, old, 0);
+ /* This ensures only one fellow resets the stat */
+ if (ret == old)
+ memset(&spinlock_stats, 0, sizeof(spinlock_stats));
+ }
+}
+
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+ check_zero();
+ spinlock_stats.contention_stats[var] += val;
+}
+
+static inline u64 spin_time_start(void)
+{
+ return xen_clocksource_read();
+}
+
+static void __spin_time_accum(u64 delta, u32 *array)
+{
+ unsigned index = ilog2(delta);
+
+ check_zero();
+
+ if (index < HISTO_BUCKETS)
+ array[index]++;
+ else
+ array[HISTO_BUCKETS]++;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+ u32 delta = xen_clocksource_read() - start;
+
+ __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
+ spinlock_stats.time_blocked += delta;
+}
+#else /* !CONFIG_XEN_DEBUG_FS */
+static inline void add_stats(enum xen_contention_stat var, u32 val)
+{
+}
+
+static inline u64 spin_time_start(void)
+{
+ return 0;
+}
+
+static inline void spin_time_accum_blocked(u64 start)
+{
+}
+#endif /* CONFIG_XEN_DEBUG_FS */
+
+struct xen_lock_waiting {
+ struct arch_spinlock *lock;
+ __ticket_t want;
+};
+
+static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
+static DEFINE_PER_CPU(char *, irq_name);
+static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
+static cpumask_t waiting_cpus;
+
+static bool xen_pvspin = true;
+__visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
+{
+ int irq = __this_cpu_read(lock_kicker_irq);
+ struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
+ int cpu = smp_processor_id();
+ u64 start;
+ __ticket_t head;
+ unsigned long flags;
+
+ /* If kicker interrupts not initialized yet, just spin */
+ if (irq == -1)
+ return;
+
+ start = spin_time_start();
+
+ /*
+ * Make sure an interrupt handler can't upset things in a
+ * partially setup state.
+ */
+ local_irq_save(flags);
+ /*
+ * We don't really care if we're overwriting some other
+ * (lock,want) pair, as that would mean that we're currently
+ * in an interrupt context, and the outer context had
+ * interrupts enabled. That has already kicked the VCPU out
+ * of xen_poll_irq(), so it will just return spuriously and
+ * retry with newly setup (lock,want).
+ *
+ * The ordering protocol on this is that the "lock" pointer
+ * may only be set non-NULL if the "want" ticket is correct.
+ * If we're updating "want", we must first clear "lock".
+ */
+ w->lock = NULL;
+ smp_wmb();
+ w->want = want;
+ smp_wmb();
+ w->lock = lock;
+
+ /* This uses set_bit, which atomic and therefore a barrier */
+ cpumask_set_cpu(cpu, &waiting_cpus);
+ add_stats(TAKEN_SLOW, 1);
+
+ /* clear pending */
+ xen_clear_irq_pending(irq);
+
+ /* Only check lock once pending cleared */
+ barrier();
+
+ /*
+ * Mark entry to slowpath before doing the pickup test to make
+ * sure we don't deadlock with an unlocker.
+ */
+ __ticket_enter_slowpath(lock);
+
+ /* make sure enter_slowpath, which is atomic does not cross the read */
+ smp_mb__after_atomic();
+
+ /*
+ * check again make sure it didn't become free while
+ * we weren't looking
+ */
+ head = READ_ONCE(lock->tickets.head);
+ if (__tickets_equal(head, want)) {
+ add_stats(TAKEN_SLOW_PICKUP, 1);
+ goto out;
+ }
+
+ /* Allow interrupts while blocked */
+ local_irq_restore(flags);
+
+ /*
+ * If an interrupt happens here, it will leave the wakeup irq
+ * pending, which will cause xen_poll_irq() to return
+ * immediately.
+ */
+
+ /* Block until irq becomes pending (or perhaps a spurious wakeup) */
+ xen_poll_irq(irq);
+ add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
+
+ local_irq_save(flags);
+
+ kstat_incr_irq_this_cpu(irq);
+out:
+ cpumask_clear_cpu(cpu, &waiting_cpus);
+ w->lock = NULL;
+
+ local_irq_restore(flags);
+
+ spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
+
+static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
+{
+ int cpu;
+
+ add_stats(RELEASED_SLOW, 1);
+
+ for_each_cpu(cpu, &waiting_cpus) {
+ const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+
+ /* Make sure we read lock before want */
+ if (READ_ONCE(w->lock) == lock &&
+ READ_ONCE(w->want) == next) {
+ add_stats(RELEASED_SLOW_KICKED, 1);
+ xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
+ break;
+ }
+ }
+}
+
+static irqreturn_t dummy_handler(int irq, void *dev_id)
+{
+ BUG();
+ return IRQ_HANDLED;
+}
+
+void xen_init_lock_cpu(int cpu)
+{
+ int irq;
+ char *name;
+
+ if (!xen_pvspin)
+ return;
+
+ WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
+ cpu, per_cpu(lock_kicker_irq, cpu));
+
+ name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
+ irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
+ cpu,
+ dummy_handler,
+ IRQF_PERCPU|IRQF_NOBALANCING,
+ name,
+ NULL);
+
+ if (irq >= 0) {
+ disable_irq(irq); /* make sure it's never delivered */
+ per_cpu(lock_kicker_irq, cpu) = irq;
+ per_cpu(irq_name, cpu) = name;
+ }
+
+ printk("cpu %d spinlock event irq %d\n", cpu, irq);
+}
+
+void xen_uninit_lock_cpu(int cpu)
+{
+ if (!xen_pvspin)
+ return;
+
+ unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
+ per_cpu(lock_kicker_irq, cpu) = -1;
+ kfree(per_cpu(irq_name, cpu));
+ per_cpu(irq_name, cpu) = NULL;
+}
+
+
+/*
+ * Our init of PV spinlocks is split in two init functions due to us
+ * using paravirt patching and jump labels patching and having to do
+ * all of this before SMP code is invoked.
+ *
+ * The paravirt patching needs to be done _before_ the alternative asm code
+ * is started, otherwise we would not patch the core kernel code.
+ */
+void __init xen_init_spinlocks(void)
+{
+
+ if (!xen_pvspin) {
+ printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
+ return;
+ }
+ printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
+ pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
+ pv_lock_ops.unlock_kick = xen_unlock_kick;
+}
+
+/*
+ * While the jump_label init code needs to happend _after_ the jump labels are
+ * enabled and before SMP is started. Hence we use pre-SMP initcall level
+ * init. We cannot do it in xen_init_spinlocks as that is done before
+ * jump labels are activated.
+ */
+static __init int xen_init_spinlocks_jump(void)
+{
+ if (!xen_pvspin)
+ return 0;
+
+ if (!xen_domain())
+ return 0;
+
+ static_key_slow_inc(&paravirt_ticketlocks_enabled);
+ return 0;
+}
+early_initcall(xen_init_spinlocks_jump);
+
+static __init int xen_parse_nopvspin(char *arg)
+{
+ xen_pvspin = false;
+ return 0;
+}
+early_param("xen_nopvspin", xen_parse_nopvspin);
+
+#ifdef CONFIG_XEN_DEBUG_FS
+
+static struct dentry *d_spin_debug;
+
+static int __init xen_spinlock_debugfs(void)
+{
+ struct dentry *d_xen = xen_init_debugfs();
+
+ if (d_xen == NULL)
+ return -ENOMEM;
+
+ if (!xen_pvspin)
+ return 0;
+
+ d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
+
+ debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
+
+ debugfs_create_u32("taken_slow", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[TAKEN_SLOW]);
+ debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
+ debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
+
+ debugfs_create_u32("released_slow", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[RELEASED_SLOW]);
+ debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
+ &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
+
+ debugfs_create_u64("time_blocked", 0444, d_spin_debug,
+ &spinlock_stats.time_blocked);
+
+ debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
+ spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
+
+ return 0;
+}
+fs_initcall(xen_spinlock_debugfs);
+
+#endif /* CONFIG_XEN_DEBUG_FS */