23b45eb9a89ce4d56f8a73e181d004b107dc1f81
[sfrench/cifs-2.6.git] / arch / x86 / xen / spinlock.c
1 /*
2  * Split spinlock implementation out into its own file, so it can be
3  * compiled in a FTRACE-compatible way.
4  */
5 #include <linux/kernel_stat.h>
6 #include <linux/spinlock.h>
7 #include <linux/debugfs.h>
8 #include <linux/log2.h>
9 #include <linux/gfp.h>
10 #include <linux/slab.h>
11
12 #include <asm/paravirt.h>
13
14 #include <xen/interface/xen.h>
15 #include <xen/events.h>
16
17 #include "xen-ops.h"
18 #include "debugfs.h"
19
20 enum xen_contention_stat {
21         TAKEN_SLOW,
22         TAKEN_SLOW_PICKUP,
23         TAKEN_SLOW_SPURIOUS,
24         RELEASED_SLOW,
25         RELEASED_SLOW_KICKED,
26         NR_CONTENTION_STATS
27 };
28
29
30 #ifdef CONFIG_XEN_DEBUG_FS
31 #define HISTO_BUCKETS   30
32 static struct xen_spinlock_stats
33 {
34         u32 contention_stats[NR_CONTENTION_STATS];
35         u32 histo_spin_blocked[HISTO_BUCKETS+1];
36         u64 time_blocked;
37 } spinlock_stats;
38
39 static u8 zero_stats;
40
41 static inline void check_zero(void)
42 {
43         u8 ret;
44         u8 old = ACCESS_ONCE(zero_stats);
45         if (unlikely(old)) {
46                 ret = cmpxchg(&zero_stats, old, 0);
47                 /* This ensures only one fellow resets the stat */
48                 if (ret == old)
49                         memset(&spinlock_stats, 0, sizeof(spinlock_stats));
50         }
51 }
52
53 static inline void add_stats(enum xen_contention_stat var, u32 val)
54 {
55         check_zero();
56         spinlock_stats.contention_stats[var] += val;
57 }
58
59 static inline u64 spin_time_start(void)
60 {
61         return xen_clocksource_read();
62 }
63
64 static void __spin_time_accum(u64 delta, u32 *array)
65 {
66         unsigned index = ilog2(delta);
67
68         check_zero();
69
70         if (index < HISTO_BUCKETS)
71                 array[index]++;
72         else
73                 array[HISTO_BUCKETS]++;
74 }
75
76 static inline void spin_time_accum_blocked(u64 start)
77 {
78         u32 delta = xen_clocksource_read() - start;
79
80         __spin_time_accum(delta, spinlock_stats.histo_spin_blocked);
81         spinlock_stats.time_blocked += delta;
82 }
83 #else  /* !CONFIG_XEN_DEBUG_FS */
84 static inline void add_stats(enum xen_contention_stat var, u32 val)
85 {
86 }
87
88 static inline u64 spin_time_start(void)
89 {
90         return 0;
91 }
92
93 static inline void spin_time_accum_blocked(u64 start)
94 {
95 }
96 #endif  /* CONFIG_XEN_DEBUG_FS */
97
98 struct xen_lock_waiting {
99         struct arch_spinlock *lock;
100         __ticket_t want;
101 };
102
103 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
104 static DEFINE_PER_CPU(char *, irq_name);
105 static DEFINE_PER_CPU(struct xen_lock_waiting, lock_waiting);
106 static cpumask_t waiting_cpus;
107
108 static bool xen_pvspin = true;
109 __visible void xen_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
110 {
111         int irq = __this_cpu_read(lock_kicker_irq);
112         struct xen_lock_waiting *w = this_cpu_ptr(&lock_waiting);
113         int cpu = smp_processor_id();
114         u64 start;
115         unsigned long flags;
116
117         /* If kicker interrupts not initialized yet, just spin */
118         if (irq == -1)
119                 return;
120
121         start = spin_time_start();
122
123         /*
124          * Make sure an interrupt handler can't upset things in a
125          * partially setup state.
126          */
127         local_irq_save(flags);
128         /*
129          * We don't really care if we're overwriting some other
130          * (lock,want) pair, as that would mean that we're currently
131          * in an interrupt context, and the outer context had
132          * interrupts enabled.  That has already kicked the VCPU out
133          * of xen_poll_irq(), so it will just return spuriously and
134          * retry with newly setup (lock,want).
135          *
136          * The ordering protocol on this is that the "lock" pointer
137          * may only be set non-NULL if the "want" ticket is correct.
138          * If we're updating "want", we must first clear "lock".
139          */
140         w->lock = NULL;
141         smp_wmb();
142         w->want = want;
143         smp_wmb();
144         w->lock = lock;
145
146         /* This uses set_bit, which atomic and therefore a barrier */
147         cpumask_set_cpu(cpu, &waiting_cpus);
148         add_stats(TAKEN_SLOW, 1);
149
150         /* clear pending */
151         xen_clear_irq_pending(irq);
152
153         /* Only check lock once pending cleared */
154         barrier();
155
156         /*
157          * Mark entry to slowpath before doing the pickup test to make
158          * sure we don't deadlock with an unlocker.
159          */
160         __ticket_enter_slowpath(lock);
161
162         /*
163          * check again make sure it didn't become free while
164          * we weren't looking
165          */
166         if (ACCESS_ONCE(lock->tickets.head) == want) {
167                 add_stats(TAKEN_SLOW_PICKUP, 1);
168                 goto out;
169         }
170
171         /* Allow interrupts while blocked */
172         local_irq_restore(flags);
173
174         /*
175          * If an interrupt happens here, it will leave the wakeup irq
176          * pending, which will cause xen_poll_irq() to return
177          * immediately.
178          */
179
180         /* Block until irq becomes pending (or perhaps a spurious wakeup) */
181         xen_poll_irq(irq);
182         add_stats(TAKEN_SLOW_SPURIOUS, !xen_test_irq_pending(irq));
183
184         local_irq_save(flags);
185
186         kstat_incr_irq_this_cpu(irq);
187 out:
188         cpumask_clear_cpu(cpu, &waiting_cpus);
189         w->lock = NULL;
190
191         local_irq_restore(flags);
192
193         spin_time_accum_blocked(start);
194 }
195 PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
196
197 static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
198 {
199         int cpu;
200
201         add_stats(RELEASED_SLOW, 1);
202
203         for_each_cpu(cpu, &waiting_cpus) {
204                 const struct xen_lock_waiting *w = &per_cpu(lock_waiting, cpu);
205
206                 /* Make sure we read lock before want */
207                 if (ACCESS_ONCE(w->lock) == lock &&
208                     ACCESS_ONCE(w->want) == next) {
209                         add_stats(RELEASED_SLOW_KICKED, 1);
210                         xen_send_IPI_one(cpu, XEN_SPIN_UNLOCK_VECTOR);
211                         break;
212                 }
213         }
214 }
215
216 static irqreturn_t dummy_handler(int irq, void *dev_id)
217 {
218         BUG();
219         return IRQ_HANDLED;
220 }
221
222 void xen_init_lock_cpu(int cpu)
223 {
224         int irq;
225         char *name;
226
227         if (!xen_pvspin)
228                 return;
229
230         WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
231              cpu, per_cpu(lock_kicker_irq, cpu));
232
233         name = kasprintf(GFP_KERNEL, "spinlock%d", cpu);
234         irq = bind_ipi_to_irqhandler(XEN_SPIN_UNLOCK_VECTOR,
235                                      cpu,
236                                      dummy_handler,
237                                      IRQF_PERCPU|IRQF_NOBALANCING,
238                                      name,
239                                      NULL);
240
241         if (irq >= 0) {
242                 disable_irq(irq); /* make sure it's never delivered */
243                 per_cpu(lock_kicker_irq, cpu) = irq;
244                 per_cpu(irq_name, cpu) = name;
245         }
246
247         printk("cpu %d spinlock event irq %d\n", cpu, irq);
248 }
249
250 void xen_uninit_lock_cpu(int cpu)
251 {
252         if (!xen_pvspin)
253                 return;
254
255         unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
256         per_cpu(lock_kicker_irq, cpu) = -1;
257         kfree(per_cpu(irq_name, cpu));
258         per_cpu(irq_name, cpu) = NULL;
259 }
260
261
262 /*
263  * Our init of PV spinlocks is split in two init functions due to us
264  * using paravirt patching and jump labels patching and having to do
265  * all of this before SMP code is invoked.
266  *
267  * The paravirt patching needs to be done _before_ the alternative asm code
268  * is started, otherwise we would not patch the core kernel code.
269  */
270 void __init xen_init_spinlocks(void)
271 {
272
273         if (!xen_pvspin) {
274                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
275                 return;
276         }
277         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
278         pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
279         pv_lock_ops.unlock_kick = xen_unlock_kick;
280 }
281
282 /*
283  * While the jump_label init code needs to happend _after_ the jump labels are
284  * enabled and before SMP is started. Hence we use pre-SMP initcall level
285  * init. We cannot do it in xen_init_spinlocks as that is done before
286  * jump labels are activated.
287  */
288 static __init int xen_init_spinlocks_jump(void)
289 {
290         if (!xen_pvspin)
291                 return 0;
292
293         if (!xen_domain())
294                 return 0;
295
296         static_key_slow_inc(&paravirt_ticketlocks_enabled);
297         return 0;
298 }
299 early_initcall(xen_init_spinlocks_jump);
300
301 static __init int xen_parse_nopvspin(char *arg)
302 {
303         xen_pvspin = false;
304         return 0;
305 }
306 early_param("xen_nopvspin", xen_parse_nopvspin);
307
308 #ifdef CONFIG_XEN_DEBUG_FS
309
310 static struct dentry *d_spin_debug;
311
312 static int __init xen_spinlock_debugfs(void)
313 {
314         struct dentry *d_xen = xen_init_debugfs();
315
316         if (d_xen == NULL)
317                 return -ENOMEM;
318
319         if (!xen_pvspin)
320                 return 0;
321
322         d_spin_debug = debugfs_create_dir("spinlocks", d_xen);
323
324         debugfs_create_u8("zero_stats", 0644, d_spin_debug, &zero_stats);
325
326         debugfs_create_u32("taken_slow", 0444, d_spin_debug,
327                            &spinlock_stats.contention_stats[TAKEN_SLOW]);
328         debugfs_create_u32("taken_slow_pickup", 0444, d_spin_debug,
329                            &spinlock_stats.contention_stats[TAKEN_SLOW_PICKUP]);
330         debugfs_create_u32("taken_slow_spurious", 0444, d_spin_debug,
331                            &spinlock_stats.contention_stats[TAKEN_SLOW_SPURIOUS]);
332
333         debugfs_create_u32("released_slow", 0444, d_spin_debug,
334                            &spinlock_stats.contention_stats[RELEASED_SLOW]);
335         debugfs_create_u32("released_slow_kicked", 0444, d_spin_debug,
336                            &spinlock_stats.contention_stats[RELEASED_SLOW_KICKED]);
337
338         debugfs_create_u64("time_blocked", 0444, d_spin_debug,
339                            &spinlock_stats.time_blocked);
340
341         debugfs_create_u32_array("histo_blocked", 0444, d_spin_debug,
342                                 spinlock_stats.histo_spin_blocked, HISTO_BUCKETS + 1);
343
344         return 0;
345 }
346 fs_initcall(xen_spinlock_debugfs);
347
348 #endif  /* CONFIG_XEN_DEBUG_FS */