Fix IO performance regression in sparc

Replace signalfd with signal handler/pipe.  There is no way to interrupt
the CPU execution loop when a file descriptor becomes readable.  This
results in a large performance regression in sparc emulation during
bootup.
   
This patch switches us to signal handler/pipe which was originally
suggested by Ian Jackson.  The signal handler lets us interrupt the
CPU emulation loop while the write to a pipe lets us avoid the
select/signal race condition.
    
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5451 c046a42c-6fe2-441c-8c8c-71466251a162

vl.c

@@ -7475,6 +7475,19 @@ static int ram_load(QEMUFile *f, void *opaque, int version_id)
     return 0;
 }
 
+void qemu_service_io(void)
+{
+    CPUState *env = cpu_single_env;
+    if (env) {
+        cpu_interrupt(env, CPU_INTERRUPT_EXIT);
+#ifdef USE_KQEMU
+        if (env->kqemu_enabled) {
+            kqemu_cpu_interrupt(env);
+        }
+#endif
+    }
+}
+
 /***********************************************************/
 /* bottom halves (can be seen as timers which expire ASAP) */