multicalls.c revision 7ebed39ff7eec204850736a662828da0b942b8c0 
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
25#include <asm/xen/hypercall.h>
26
27#include "multicalls.h"
28
29#define MC_DEBUG	1
30
31#define MC_BATCH	32
32#define MC_ARGS		(MC_BATCH * 16 / sizeof(u64))
33
34struct mc_buffer {
35	struct multicall_entry entries[MC_BATCH];
36#if MC_DEBUG
37	struct multicall_entry debug[MC_BATCH];
38#endif
39	u64 args[MC_ARGS];
40	struct callback {
41		void (*fn)(void *);
42		void *data;
43	} callbacks[MC_BATCH];
44	unsigned mcidx, argidx, cbidx;
45};
46
47static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
48DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
49
50void xen_mc_flush(void)
51{
52	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
53	int ret = 0;
54	unsigned long flags;
55	int i;
56
57	BUG_ON(preemptible());
58
59	/* Disable interrupts in case someone comes in and queues
60	   something in the middle */
61	local_irq_save(flags);
62
63	if (b->mcidx) {
64#if MC_DEBUG
65		memcpy(b->debug, b->entries,
66		       b->mcidx * sizeof(struct multicall_entry));
67#endif
68
69		if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
70			BUG();
71		for (i = 0; i < b->mcidx; i++)
72			if (b->entries[i].result < 0)
73				ret++;
74
75#if MC_DEBUG
76		if (ret) {
77			printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
78			       ret, smp_processor_id());
79			for (i = 0; i < b->mcidx; i++) {
80				printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
81				       i+1, b->mcidx,
82				       b->debug[i].op,
83				       b->debug[i].args[0],
84				       b->entries[i].result);
85			}
86		}
87#endif
88
89		b->mcidx = 0;
90		b->argidx = 0;
91	} else
92		BUG_ON(b->argidx != 0);
93
94	local_irq_restore(flags);
95
96	for (i = 0; i < b->cbidx; i++) {
97		struct callback *cb = &b->callbacks[i];
98
99		(*cb->fn)(cb->data);
100	}
101	b->cbidx = 0;
102
103	BUG_ON(ret);
104}
105
106struct multicall_space __xen_mc_entry(size_t args)
107{
108	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
109	struct multicall_space ret;
110	unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
111
112	BUG_ON(preemptible());
113	BUG_ON(argspace > MC_ARGS);
114
115	if (b->mcidx == MC_BATCH ||
116	    (b->argidx + argspace) > MC_ARGS)
117		xen_mc_flush();
118
119	ret.mc = &b->entries[b->mcidx];
120	b->mcidx++;
121	ret.args = &b->args[b->argidx];
122	b->argidx += argspace;
123
124	return ret;
125}
126
127void xen_mc_callback(void (*fn)(void *), void *data)
128{
129	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
130	struct callback *cb;
131
132	if (b->cbidx == MC_BATCH)
133		xen_mc_flush();
134
135	cb = &b->callbacks[b->cbidx++];
136	cb->fn = fn;
137	cb->data = data;
138}
139