/*
* Xen hypercall batching.
*
* Xen allows multiple hypercalls to be issued at once, using the
* multicall interface. This allows the cost of trapping into the
* hypervisor to be amortized over several calls.
*
* This file implements a simple interface for multicalls. There's a
* per-cpu buffer of outstanding multicalls. When you want to queue a
* multicall for issuing, you can allocate a multicall slot for the
* call and its arguments, along with storage for space which is
* pointed to by the arguments (for passing pointers to structures,
* etc). When the multicall is actually issued, all the space for the
* commands and allocated memory is freed for reuse.
*
* Multicalls are flushed whenever any of the buffers get full, or
* when explicitly requested. There's no way to get per-multicall
* return results back. It will BUG if any of the multicalls fail.
*
* Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
*/
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/debugfs.h>
#include <asm/xen/hypercall.h>
#include "multicalls.h"
#include "debugfs.h"
#define MC_BATCH 32
#define MC_DEBUG 1
#define MC_ARGS (MC_BATCH * 16)
struct mc_buffer {
struct multicall_entry entries[MC_BATCH];
#if MC_DEBUG
struct multicall_entry debug[MC_BATCH];
void *caller[MC_BATCH];
#endif
unsigned char args[MC_ARGS];
struct callback {
void (*fn)(void *);
void *data;
} callbacks[MC_BATCH];
unsigned mcidx, argidx, cbidx;
};
static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
/* flush reasons 0- slots, 1- args, 2- callbacks */
enum flush_reasons
{
FL_SLOTS,
FL_ARGS,
FL_CALLBACKS,
FL_N_REASONS
};
#ifdef CONFIG_XEN_DEBUG_FS
#define NHYPERCALLS 40 /* not really */
static struct {
unsigned histo[MC_BATCH+1];
unsigned issued;
unsigned arg_total;
unsigned hypercalls;
unsigned histo_hypercalls[NHYPERCALLS];
unsigned flush[FL_N_REASONS];
} mc_stats;
static u8 zero_stats;
static inline void check_zero(void)
{
if (unlikely(zero_stats)) {
memset(&mc_stats, 0, sizeof(mc_stats));
zero_stats = 0;
}
}
static void mc_add_stats(const struct mc_buffer *mc)
{
int i;
check_zero();
mc_stats.issued++;
mc_stats.hypercalls += mc->mcidx;
mc_stats.arg_total += mc->argidx;
mc_stats.histo[mc->mcidx]++;
for(i = 0; i < mc->mcidx; i++) {
unsigned op = mc->entries[i].op;
if (op < NHYPERCALLS)
mc_stats.histo_hypercalls[op]++;
}
}
static void mc_stats_flush(enum flush_reasons idx)
{
check_zero();
mc_stats.flush[idx]++;
}
#else /* !CONFIG_XEN_DEBUG_FS */
static inline void mc_add_stats(const struct mc_buffer *mc)
{
}
static inline void mc_stats_flush(enum flush_reasons idx)
{
}
#endif /* CONFIG_XEN_DEBUG_FS */
void xen_mc_flush(void)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
int ret = 0;
unsigned long flags;
int i;
BUG_ON(preemptible());
/* Disable interrupts in case someone comes in and queues
something in the middle */
local_irq_save(flags);
mc_add_stats(b);
if (b->mcidx) {
#if MC_DEBUG
memcpy(b->debug, b->entries,
b->mcidx * sizeof(struct multicall_entry));
#endif
if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
BUG();
for (i = 0; i < b->mcidx; i++)
if (b->entries[i].result < 0)
ret++;
#if MC_DEBUG
if (ret) {
printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
ret, smp_processor_id());
dump_stack();
for (i = 0; i < b->mcidx; i++) {
printk(KERN_DEBUG " call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
i+1, b->mcidx,
b->debug[i].op,
b->debug[i].args[0],
b->entries[i].result,
b->caller[i]);
}
}
#endif
b->mcidx = 0;
b->argidx = 0;
} else
BUG_ON(b->argidx != 0);
for (i = 0; i < b->cbidx; i++) {
struct callback *cb = &b->callbacks[i];
(*cb->fn)(cb->data);
}
b->cbidx = 0;
local_irq_restore(flags);
WARN_ON(ret);
}
struct multicall_space __xen_mc_entry(size_t args)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
struct multicall_space ret;
unsigned argidx = roundup(b->argidx, sizeof(u64));
BUG_ON(preemptible());
BUG_ON(b->argidx >= MC_ARGS);
if (b->mcidx == MC_BATCH ||
(argidx + args) >= MC_ARGS) {
mc_stats_flush(b->mcidx == MC_BATCH ? FL_SLOTS : FL_ARGS);
xen_mc_flush();
argidx = roundup(b->argidx, sizeof(u64));
}
ret.mc = &b->entries[b->mcidx];
#ifdef MC_DEBUG
b->caller[b->mcidx] = __builtin_return_address(0);
#endif
b->mcidx++;
ret.args = &b->args[argidx];
b->argidx = argidx + args;
BUG_ON(b->argidx >= MC_ARGS);
return ret;
}
struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
struct multicall_space ret = { NULL, NULL };
BUG_ON(preemptible());
BUG_ON(b->argidx >= MC_ARGS);
if (b->mcidx == 0)
return ret;
if (b->entries[b->mcidx - 1].op != op)
return ret;
if ((b->argidx + size) >= MC_ARGS)
return ret;
ret.mc = &b->entries[b->mcidx - 1];
ret.args = &b->args[b->argidx];
b->argidx += size;
BUG_ON(b->argidx >= MC_ARGS);
return ret;
}
void xen_mc_callback(void (*fn)(void *), void *data)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
struct callback *cb;
if (b->cbidx == MC_BATCH) {
mc_stats_flush(FL_CALLBACKS);
xen_mc_flush();
}
cb = &b->callbacks[b->cbidx++];
cb->fn = fn;
cb->data = data;
}
#ifdef CONFIG_XEN_DEBUG_FS
static struct dentry *d_mc_debug;
static int __init xen_mc_debugfs(void)
{
struct dentry *d_xen = xen_init_debugfs();
if (d_xen == NULL)
return -ENOMEM;
d_mc_debug = debugfs_create_dir("multicalls", d_xen);
debugfs_create_u8("zero_stats", 0644, d_mc_debug, &zero_stats);
debugfs_create_u32("batches", 0444, d_mc_debug, &mc_stats.issued);
debugfs_create_u32("hypercalls", 0444, d_mc_debug, &mc_stats.hypercalls);
debugfs_create_u32("arg_total", 0444, d_mc_debug, &mc_stats.arg_total);
xen_debugfs_create_u32_array("batch_histo", 0444, d_mc_debug,
mc_stats.histo, MC_BATCH);
xen_debugfs_create_u32_array("hypercall_histo", 0444, d_mc_debug,
mc_stats.histo_hypercalls, NHYPERCALLS);
xen_debugfs_create_u32_array("flush_reasons", 0444, d_mc_debug,
mc_stats.flush, FL_N_REASONS);
return 0;
}
fs_initcall(xen_mc_debugfs);
#endif /* CONFIG_XEN_DEBUG_FS */
