Re: [Qemu-devel] [PATCH] Improve -net user (slirp) performance by 4x

[Fabrice Bellard]

Ed Swierk wrote:

> 3. qemu sleeps soundly while packets back up in slirp's buffers. slirp
> socket fds should be added to the main qemu select() loop to avoid
> unnecessary delays.

I agree, but your patch does not suppress the slirp select(). I tried to 
do it with the following patch but slirp becomes twice slower and I 
cannot get a good explanation. Maybe you could look at that problem so 
that a real correction can be commited.

Regards,

Fabrice.

Index: vl.c
===================================================================
RCS file: /sources/qemu/qemu/vl.c,v
retrieving revision 1.180
diff -u -w -r1.180 vl.c
--- vl.c        30 Apr 2006 22:53:25 -0000      1.180
+++ vl.c        1 May 2006 12:17:36 -0000
@@ -4361,7 +4361,7 @@
 void main_loop_wait(int timeout)
 {
     IOHandlerRecord *ioh, *ioh_next;
-    fd_set rfds, wfds;
+    fd_set rfds, wfds, xfds;
     int ret, nfds;
     struct timeval tv;
     PollingEntry *pe;
@@ -4382,6 +4382,7 @@
     nfds = -1;
     FD_ZERO(&rfds);
     FD_ZERO(&wfds);
+    FD_ZERO(&xfds);
     for(ioh = first_io_handler; ioh != NULL; ioh = ioh->next) {
         if (ioh->fd_read &&
             (!ioh->fd_read_poll ||
@@ -4403,7 +4404,12 @@
 #else
     tv.tv_usec = timeout * 1000;
 #endif
-    ret = select(nfds + 1, &rfds, &wfds, NULL, &tv);
+#if defined(CONFIG_SLIRP)
+    if (slirp_inited) {
+        slirp_select_fill(&nfds, &rfds, &wfds, &xfds);
+    }
+#endif
+    ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv);
     if (ret > 0) {
         /* XXX: better handling of removal */
         for(ioh = first_io_handler; ioh != NULL; ioh = ioh_next) {
@@ -4416,29 +4422,13 @@
             }
         }
     }
-#ifdef _WIN32
-    tap_win32_poll();
-#endif
-
 #if defined(CONFIG_SLIRP)
-    /* XXX: merge with the previous select() */
-    if (slirp_inited) {
-        fd_set rfds, wfds, xfds;
-        int nfds;
-        struct timeval tv;
-
-        nfds = -1;
-        FD_ZERO(&rfds);
-        FD_ZERO(&wfds);
-        FD_ZERO(&xfds);
-        slirp_select_fill(&nfds, &rfds, &wfds, &xfds);
-        tv.tv_sec = 0;
-        tv.tv_usec = 0;
-        ret = select(nfds + 1, &rfds, &wfds, &xfds, &tv);
-        if (ret >= 0) {
+    if (slirp_inited && ret >= 0) {
             slirp_select_poll(&rfds, &wfds, &xfds);
         }
-    }
+#endif
+#ifdef _WIN32
+    tap_win32_poll();
 #endif

     if (vm_running) {