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>

diff --git a/sysemu.h b/sysemu.h
index bd830e51490e8171aabd69d76e68e81866d76463..909045788135cdd9268fd9c65c8072ef4ced6765 100644 (file)
--- a/sysemu.h
+++ b/sysemu.h
@@ -67,7 +67,7 @@ void do_info_snapshots(Monitor *mon);
 
 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,

diff --git a/vl.c b/vl.c
index c52937a151d148c23f08683ffff52d8787f1f298..9cd67a37465a685f5501577a7a87b64ce3445065 100644 (file)
--- a/vl.c
+++ b/vl.c
@@ -1321,7 +1321,7 @@ void qemu_system_vmstop_request(int reason)
     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 @@ void main_loop_wait(int nonblocking)
        them.  */
     qemu_bh_poll();
 
+    return ret;
 }
 
 #ifndef CONFIG_IOTHREAD
@@ -1385,7 +1386,8 @@ qemu_irq qemu_system_powerdown;
 
 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 @@ static void main_loop(void)
     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 @@ static void main_loop(void)
 #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