commit c9f711a5d31e22dac932c1c01e9c0f97caff0988
author Jan Kiszka <jan.kiszka@siemens.com> Mon Aug 22 17:46:02 2011 +0200
committer Anthony Liguori <aliguori@us.ibm.com> Mon Aug 22 14:37:02 2011 -0500
tree 1d7b980c02326f221d70778ca1e7798e66439d24
parent 200668ba0839e664f0e4d0bcdc55ab5a163a418a

Poll main loop after I/O events were received

Polling until select returns empty fdsets helps to reduce the switches
between iothread and vcpus. The benefit of this patch is best visible
when running an SMP guest on an SMP host in emulation mode.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

sysemu.h

diff --git a/sysemu.h b/sysemu.h
index bd830e5..9090457 100644
--- a/sysemu.h
+++ b/sysemu.h
@@ -67,7 +67,7 @@
 
 void qemu_announce_self(void);
 
-void main_loop_wait(int nonblocking);
+int main_loop_wait(int nonblocking);
 
 bool qemu_savevm_state_blocked(Monitor *mon);
 int qemu_savevm_state_begin(Monitor *mon, QEMUFile *f, int blk_enable,

vl.c

diff --git a/vl.c b/vl.c
index c52937a..9cd67a3 100644
--- a/vl.c
+++ b/vl.c
@@ -1321,7 +1321,7 @@
     qemu_notify_event();
 }
 
-void main_loop_wait(int nonblocking)
+int main_loop_wait(int nonblocking)
 {
     fd_set rfds, wfds, xfds;
     int ret, nfds;
@@ -1368,6 +1368,7 @@
        them.  */
     qemu_bh_poll();
 
+    return ret;
 }
 
 #ifndef CONFIG_IOTHREAD
@@ -1385,7 +1386,8 @@
 
 static void main_loop(void)
 {
-    bool nonblocking = false;
+    bool nonblocking;
+    int last_io __attribute__ ((unused)) = 0;
 #ifdef CONFIG_PROFILER
     int64_t ti;
 #endif
@@ -1394,7 +1396,9 @@
     qemu_main_loop_start();
 
     for (;;) {
-#ifndef CONFIG_IOTHREAD
+#ifdef CONFIG_IOTHREAD
+        nonblocking = !kvm_enabled() && last_io > 0;
+#else
         nonblocking = cpu_exec_all();
         if (vm_request_pending()) {
             nonblocking = true;
@@ -1403,7 +1407,7 @@
 #ifdef CONFIG_PROFILER
         ti = profile_getclock();
 #endif
-        main_loop_wait(nonblocking);
+        last_io = main_loop_wait(nonblocking);
 #ifdef CONFIG_PROFILER
         dev_time += profile_getclock() - ti;
 #endif