[deliverable/linux.git] / arch / i386 / xen / multicalls.c

/*
 * 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 <asm/xen/hypercall.h>

#include "multicalls.h"

#define MC_BATCH	8
#define MC_ARGS		(MC_BATCH * 32 / sizeof(u64))

struct mc_buffer {
	struct multicall_entry entries[MC_BATCH];
	u64 args[MC_ARGS];
	unsigned mcidx, argidx;
};

static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);

void xen_mc_flush(void)
{
	struct mc_buffer *b = &get_cpu_var(mc_buffer);
	int ret = 0;
	unsigned long flags;

	/* Disable interrupts in case someone comes in and queues
	   something in the middle */
	local_irq_save(flags);

	if (b->mcidx) {
		int i;

		if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
			BUG();
		for (i = 0; i < b->mcidx; i++)
			if (b->entries[i].result < 0)
				ret++;
		b->mcidx = 0;
		b->argidx = 0;
	} else
		BUG_ON(b->argidx != 0);

	put_cpu_var(mc_buffer);
	local_irq_restore(flags);

	BUG_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 argspace = (args + sizeof(u64) - 1) / sizeof(u64);

	BUG_ON(argspace > MC_ARGS);

	if (b->mcidx == MC_BATCH ||
	    (b->argidx + argspace) > MC_ARGS)
		xen_mc_flush();

	ret.mc = &b->entries[b->mcidx];
	b->mcidx++;
	ret.args = &b->args[b->argidx];
	b->argidx += argspace;

	put_cpu_var(mc_buffer);

	return ret;
}
Commit	Line	Data
5ead97c8 JF	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
	24	#include <asm/xen/hypercall.h>
	25
	26	#include "multicalls.h"
	27
	28	#define MC_BATCH 8
	29	#define MC_ARGS (MC_BATCH * 32 / sizeof(u64))
	30
	31	struct mc_buffer {
	32	struct multicall_entry entries[MC_BATCH];
	33	u64 args[MC_ARGS];
	34	unsigned mcidx, argidx;
	35	};
	36
	37	static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
	38	DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
	39
	40	void xen_mc_flush(void)
	41	{
	42	struct mc_buffer *b = &get_cpu_var(mc_buffer);
	43	int ret = 0;
	44	unsigned long flags;
	45
	46	/* Disable interrupts in case someone comes in and queues
	47	something in the middle */
	48	local_irq_save(flags);
	49
	50	if (b->mcidx) {
	51	int i;
	52
	53	if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
	54	BUG();
	55	for (i = 0; i < b->mcidx; i++)
	56	if (b->entries[i].result < 0)
	57	ret++;
	58	b->mcidx = 0;
	59	b->argidx = 0;
	60	} else
	61	BUG_ON(b->argidx != 0);
	62
	63	put_cpu_var(mc_buffer);
	64	local_irq_restore(flags);
65
66	BUG_ON(ret);
67	}
68
69	struct multicall_space __xen_mc_entry(size_t args)
70	{
71	struct mc_buffer *b = &get_cpu_var(mc_buffer);
72	struct multicall_space ret;
73	unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
74
75	BUG_ON(argspace > MC_ARGS);
76
77	if (b->mcidx == MC_BATCH \|\|
78	(b->argidx + argspace) > MC_ARGS)
79	xen_mc_flush();
80
81	ret.mc = &b->entries[b->mcidx];
82	b->mcidx++;
83	ret.args = &b->args[b->argidx];
84	b->argidx += argspace;
85
86	put_cpu_var(mc_buffer);
87
88	return ret;
89	}