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