multicalls.c revision 84cdee76b15f3669f012d5916287d124c805ef2f 
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
38struct mc_buffer {
39	struct multicall_entry entries[MC_BATCH];
40#if MC_DEBUG
41	struct multicall_entry debug[MC_BATCH];
42	void *caller[MC_BATCH];
43#endif
44	unsigned char args[MC_ARGS];
45	struct callback {
46		void (*fn)(void *);
47		void *data;
48	} callbacks[MC_BATCH];
49	unsigned mcidx, argidx, cbidx;
50};
51
52static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
53DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
54
55void xen_mc_flush(void)
56{
57	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
58	int ret = 0;
59	unsigned long flags;
60	int i;
61
62	BUG_ON(preemptible());
63
64	/* Disable interrupts in case someone comes in and queues
65	   something in the middle */
66	local_irq_save(flags);
67
68	if (b->mcidx) {
69#if MC_DEBUG
70		memcpy(b->debug, b->entries,
71		       b->mcidx * sizeof(struct multicall_entry));
72#endif
73
74		if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
75			BUG();
76		for (i = 0; i < b->mcidx; i++)
77			if (b->entries[i].result < 0)
78				ret++;
79
80#if MC_DEBUG
81		if (ret) {
82			printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
83			       ret, smp_processor_id());
84			dump_stack();
85			for (i = 0; i < b->mcidx; i++) {
86				printk(KERN_DEBUG "  call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
87				       i+1, b->mcidx,
88				       b->debug[i].op,
89				       b->debug[i].args[0],
90				       b->entries[i].result,
91				       b->caller[i]);
92			}
93		}
94#endif
95
96		b->mcidx = 0;
97		b->argidx = 0;
98	} else
99		BUG_ON(b->argidx != 0);
100
101	for (i = 0; i < b->cbidx; i++) {
102		struct callback *cb = &b->callbacks[i];
103
104		(*cb->fn)(cb->data);
105	}
106	b->cbidx = 0;
107
108	local_irq_restore(flags);
109
110	WARN_ON(ret);
111}
112
113struct multicall_space __xen_mc_entry(size_t args)
114{
115	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
116	struct multicall_space ret;
117	unsigned argidx = roundup(b->argidx, sizeof(u64));
118
119	BUG_ON(preemptible());
120	BUG_ON(b->argidx >= MC_ARGS);
121
122	if (b->mcidx == MC_BATCH ||
123	    (argidx + args) >= MC_ARGS) {
124		xen_mc_flush();
125		argidx = roundup(b->argidx, sizeof(u64));
126	}
127
128	ret.mc = &b->entries[b->mcidx];
129#ifdef MC_DEBUG
130	b->caller[b->mcidx] = __builtin_return_address(0);
131#endif
132	b->mcidx++;
133	ret.args = &b->args[argidx];
134	b->argidx = argidx + args;
135
136	BUG_ON(b->argidx >= MC_ARGS);
137	return ret;
138}
139
140struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
141{
142	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
143	struct multicall_space ret = { NULL, NULL };
144
145	BUG_ON(preemptible());
146	BUG_ON(b->argidx >= MC_ARGS);
147
148	if (b->mcidx == 0)
149		return ret;
150
151	if (b->entries[b->mcidx - 1].op != op)
152		return ret;
153
154	if ((b->argidx + size) >= MC_ARGS)
155		return ret;
156
157	ret.mc = &b->entries[b->mcidx - 1];
158	ret.args = &b->args[b->argidx];
159	b->argidx += size;
160
161	BUG_ON(b->argidx >= MC_ARGS);
162	return ret;
163}
164
165void xen_mc_callback(void (*fn)(void *), void *data)
166{
167	struct mc_buffer *b = &__get_cpu_var(mc_buffer);
168	struct callback *cb;
169
170	if (b->cbidx == MC_BATCH)
171		xen_mc_flush();
172
173	cb = &b->callbacks[b->cbidx++];
174	cb->fn = fn;
175	cb->data = data;
176}
177