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-rw-r--r--arch/i386/xen/multicalls.c89
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 00000000000..869f9833f08
--- /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;
+}