arch/x86/xen/multicalls.c

   1 /*
   2  * Xen hypercall batching.
   3  *
   4  * Xen allows multiple hypercalls to be issued at once, using the
   5  * multicall interface.  This allows the cost of trapping into the
   6  * hypervisor to be amortized over several calls.
   7  *
   8  * This file implements a simple interface for multicalls.  There's a
   9  * per-cpu buffer of outstanding multicalls.  When you want to queue a
  10  * multicall for issuing, you can allocate a multicall slot for the
  11  * call and its arguments, along with storage for space which is
  12  * pointed to by the arguments (for passing pointers to structures,
  13  * etc).  When the multicall is actually issued, all the space for the
  14  * commands and allocated memory is freed for reuse.
  15  *
  16  * Multicalls are flushed whenever any of the buffers get full, or
  17  * when explicitly requested.  There's no way to get per-multicall
  18  * return results back.  It will BUG if any of the multicalls fail.
  19  *
  20  * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
  21  */
  22 #include <linux/percpu.h>
  23 #include <linux/hardirq.h>
  24 #include <linux/debugfs.h>
  25
  26 #include <asm/xen/hypercall.h>
  27
  28 #include "multicalls.h"
  29 #include "debugfs.h"
  30
  31 #define MC_BATCH        32
  32
  33 #define MC_DEBUG        1
  34
  35 #define MC_ARGS         (MC_BATCH * 16)
  36
  37
  38 struct mc_buffer {
  39         struct multicall_entry entries[MC_BATCH];
  40 #if MC_DEBUG
  41         struct multicall_entry debug[MC_BATCH];
  42 #endif
  43         unsigned char args[MC_ARGS];
  44         struct callback {
  45                 void (*fn)(void *);
  46                 void *data;
  47         } callbacks[MC_BATCH];
  48         unsigned mcidx, argidx, cbidx;
  49 };
  50
  51 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
  52 DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
  53
  54 /* flush reasons 0- slots, 1- args, 2- callbacks */
  55 enum flush_reasons
  56 {
  57         FL_SLOTS,
  58         FL_ARGS,
  59         FL_CALLBACKS,
  60
  61         FL_N_REASONS
  62 };
  63
  64 #ifdef CONFIG_XEN_DEBUG_FS
  65 #define NHYPERCALLS     40              /* not really */
  66
  67 static struct {
  68         unsigned histo[MC_BATCH+1];
  69
  70         unsigned issued;
  71         unsigned arg_total;
  72         unsigned hypercalls;
  73         unsigned histo_hypercalls[NHYPERCALLS];
  74
  75         unsigned flush[FL_N_REASONS];
  76 } mc_stats;
  77
  78 static u8 zero_stats;
  79
  80 static inline void check_zero(void)
  81 {
  82         if (unlikely(zero_stats)) {
  83                 memset(&mc_stats, 0, sizeof(mc_stats));
  84                 zero_stats = 0;
  85         }
  86 }
  87
  88 static void mc_add_stats(const struct mc_buffer *mc)
  89 {
  90         int i;
  91
  92         check_zero();
  93
  94         mc_stats.issued++;
  95         mc_stats.hypercalls += mc->mcidx;
  96         mc_stats.arg_total += mc->argidx;
  97
  98         mc_stats.histo[mc->mcidx]++;
  99         for(i = 0; i < mc->mcidx; i++) {
 100                 unsigned op = mc->entries[i].op;
 101                 if (op < NHYPERCALLS)
 102                         mc_stats.histo_hypercalls[op]++;
 103         }
 104 }
 105
 106 static void mc_stats_flush(enum flush_reasons idx)
 107 {
 108         check_zero();
 109
 110         mc_stats.flush[idx]++;
 111 }
 112
 113 #else  /* !CONFIG_XEN_DEBUG_FS */
 114
 115 static inline void mc_add_stats(const struct mc_buffer *mc)
 116 {
 117 }
 118
 119 static inline void mc_stats_flush(enum flush_reasons idx)
 120 {
 121 }
 122 #endif  /* CONFIG_XEN_DEBUG_FS */
 123
 124 void xen_mc_flush(void)
 125 {
 126         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 127         int ret = 0;
 128         unsigned long flags;
 129         int i;
 130
 131         BUG_ON(preemptible());
 132
 133         /* Disable interrupts in case someone comes in and queues
 134            something in the middle */
 135         local_irq_save(flags);
 136
 137         mc_add_stats(b);
 138
 139         if (b->mcidx) {
 140 #if MC_DEBUG
 141                 memcpy(b->debug, b->entries,
 142                        b->mcidx * sizeof(struct multicall_entry));
 143 #endif
 144
 145                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
 146                         BUG();
 147                 for (i = 0; i < b->mcidx; i++)
 148                         if (b->entries[i].result < 0)
 149                                 ret++;
 150
 151 #if MC_DEBUG
 152                 if (ret) {
 153                         printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
 154                                ret, smp_processor_id());
 155                         dump_stack();
 156                         for (i = 0; i < b->mcidx; i++) {
 157                                 printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
 158                                        i+1, b->mcidx,
 159                                        b->debug[i].op,
 160                                        b->debug[i].args[0],
 161                                        b->entries[i].result);
 162                         }
 163                 }
 164 #endif
 165
 166                 b->mcidx = 0;
 167                 b->argidx = 0;
 168         } else
 169                 BUG_ON(b->argidx != 0);
 170
 171         local_irq_restore(flags);
 172
 173         for (i = 0; i < b->cbidx; i++) {
 174                 struct callback *cb = &b->callbacks[i];
 175
 176                 (*cb->fn)(cb->data);
 177         }
 178         b->cbidx = 0;
 179
 180         BUG_ON(ret);
 181 }
 182
 183 struct multicall_space __xen_mc_entry(size_t args)
 184 {
 185         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 186         struct multicall_space ret;
 187         unsigned argidx = roundup(b->argidx, sizeof(u64));
 188
 189         BUG_ON(preemptible());
 190         BUG_ON(b->argidx > MC_ARGS);
 191
 192         if (b->mcidx == MC_BATCH ||
 193             (argidx + args) > MC_ARGS) {
 194                 mc_stats_flush(b->mcidx == MC_BATCH ? FL_SLOTS : FL_ARGS);
 195                 xen_mc_flush();
 196                 argidx = roundup(b->argidx, sizeof(u64));
 197         }
 198
 199         ret.mc = &b->entries[b->mcidx];
 200         b->mcidx++;
 201         ret.args = &b->args[argidx];
 202         b->argidx = argidx + args;
 203
 204         BUG_ON(b->argidx > MC_ARGS);
 205         return ret;
 206 }
 207
 208 struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
 209 {
 210         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 211         struct multicall_space ret = { NULL, NULL };
 212
 213         BUG_ON(preemptible());
 214         BUG_ON(b->argidx > MC_ARGS);
 215
 216         if (b->mcidx == 0)
 217                 return ret;
 218
 219         if (b->entries[b->mcidx - 1].op != op)
 220                 return ret;
 221
 222         if ((b->argidx + size) > MC_ARGS)
 223                 return ret;
 224
 225         ret.mc = &b->entries[b->mcidx - 1];
 226         ret.args = &b->args[b->argidx];
 227         b->argidx += size;
 228
 229         BUG_ON(b->argidx > MC_ARGS);
 230         return ret;
 231 }
 232
 233 void xen_mc_callback(void (*fn)(void *), void *data)
 234 {
 235         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
 236         struct callback *cb;
 237
 238         if (b->cbidx == MC_BATCH) {
 239                 mc_stats_flush(FL_CALLBACKS);
 240                 xen_mc_flush();
 241         }
 242
 243         cb = &b->callbacks[b->cbidx++];
 244         cb->fn = fn;
 245         cb->data = data;
 246 }
 247
 248 #ifdef CONFIG_XEN_DEBUG_FS
 249
 250 static struct dentry *d_mc_debug;
 251
 252 static int __init xen_mc_debugfs(void)
 253 {
 254         struct dentry *d_xen = xen_init_debugfs();
 255
 256         if (d_xen == NULL)
 257                 return -ENOMEM;
 258
 259         d_mc_debug = debugfs_create_dir("multicalls", d_xen);
 260
 261         debugfs_create_u8("zero_stats", 0644, d_mc_debug, &zero_stats);
 262
 263         debugfs_create_u32("batches", 0444, d_mc_debug, &mc_stats.issued);
 264         debugfs_create_u32("hypercalls", 0444, d_mc_debug, &mc_stats.hypercalls);
 265         debugfs_create_u32("arg_total", 0444, d_mc_debug, &mc_stats.arg_total);
 266
 267         xen_debugfs_create_u32_array("batch_histo", 0444, d_mc_debug,
 268                                      mc_stats.histo, MC_BATCH);
 269         xen_debugfs_create_u32_array("hypercall_histo", 0444, d_mc_debug,
 270                                      mc_stats.histo_hypercalls, NHYPERCALLS);
 271         xen_debugfs_create_u32_array("flush_reasons", 0444, d_mc_debug,
 272                                      mc_stats.flush, FL_N_REASONS);
 273
 274         return 0;
 275 }
 276 fs_initcall(xen_mc_debugfs);
 277
 278 #endif  /* CONFIG_XEN_DEBUG_FS */