xen/multicall: special-case singleton hypercalls
Singleton calls seem to end up being pretty common, so just
directly call the hypercall rather than going via multicall.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index cc71f7c..2474553 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -55,6 +55,7 @@
void xen_mc_flush(void)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
+ struct multicall_entry *mc;
int ret = 0;
unsigned long flags;
int i;
@@ -67,7 +68,24 @@
trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
- if (b->mcidx) {
+ switch (b->mcidx) {
+ case 0:
+ /* no-op */
+ BUG_ON(b->argidx != 0);
+ break;
+
+ case 1:
+ /* Singleton multicall - bypass multicall machinery
+ and just do the call directly. */
+ mc = &b->entries[0];
+
+ mc->result = privcmd_call(mc->op,
+ mc->args[0], mc->args[1], mc->args[2],
+ mc->args[3], mc->args[4]);
+ ret = mc->result < 0;
+ break;
+
+ default:
#if MC_DEBUG
memcpy(b->debug, b->entries,
b->mcidx * sizeof(struct multicall_entry));
@@ -94,11 +112,10 @@
}
}
#endif
+ }
- b->mcidx = 0;
- b->argidx = 0;
- } else
- BUG_ON(b->argidx != 0);
+ b->mcidx = 0;
+ b->argidx = 0;
for (i = 0; i < b->cbidx; i++) {
struct callback *cb = &b->callbacks[i];