1 files changed, 89 insertions, 0 deletions

diff --git a/arch/i386/xen/multicalls.c b/arch/i386/xen/multicalls.c
new file mode 100644
index 000000000000..869f9833f08f
--- /dev/null
+++ b/arch/i386/xen/multicalls.c
@@ -0,0 +1,89 @@
+/*
+ * 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;
+}