Re: [Qemu-devel] 0.9.0 Win32 Tap inferface PPC Guest issue

[Ely Soto]

Ok this is the fix I came up with.

Basically it will check all the other
objects that could potentially be waiting for service. This will prevent
one high priority object from starving the rest.

I'm not certain what the intention for
the timeout > 0 check but this completely prevented any wait object
servicing on my machine.

The Tap interface now works smoothly
without issue.


Diff/patch for 0.9.0 release version
of vl.c 
==================================
5840c5840
<     int ret, nfds;
---
>     int ret, ret2, nfds,
i;
5851c5851
<     if (ret == 0 &&
timeout > 0) {
---
>     if (ret == 0) {
5858a5859,5873
>          
      
>          
  /* Check for additional signaled events */ 
>          
  for(i = (ret - WAIT_OBJECT_0 + 1); i < w->num; i++) {
>          
                     

>          
      /* Check if event is signaled */
>          
      ret2 = WaitForSingleObject(w->events[i], 0);
>          
      if(ret2 == WAIT_OBJECT_0) {
>          
          if (w->func[i])
>          
              w->func[i](w->opaque[i]);
>          
      } else if (ret2 == WAIT_TIMEOUT) {
>          
      } else {
>          
          err = GetLastError();
>          
          fprintf(stderr, "WaitForSingleObject
error %d %d\n", i, err);
>          
      }              
 
>          
  }                
5862c5877
<          
  fprintf(stderr, "Wait error %d %d\n", ret, err);
---
>          
  fprintf(stderr, "WaitForMultipleObjects error %d %d\n",
ret, err);
==================================


Diff/patch for version 1.279 of vl.c

==================================
6146c6146
<     int ret, nfds;
---
>     int ret, ret2, nfds,
i;
6157c6157
<     if (ret == 0 &&
timeout > 0) {
---
>     if (ret == 0) {
6164a6165,6179
>          
      
>          
  /* Check for additional signaled events */ 
>          
  for(i = (ret - WAIT_OBJECT_0 + 1); i < w->num; i++) {
>          
                     

>          
      /* Check if event is signaled */
>          
      ret2 = WaitForSingleObject(w->events[i], 0);
>          
      if(ret2 == WAIT_OBJECT_0) {
>          
          if (w->func[i])
>          
              w->func[i](w->opaque[i]);
>          
      } else if (ret2 == WAIT_TIMEOUT) {
>          
      } else {
>          
          err = GetLastError();
>          
          fprintf(stderr, "WaitForSingleObject
error %d %d\n", i, err);
>          
      }              
 
>          
  }                  

6168c6183
<          
  fprintf(stderr, "Wait error %d %d\n", ret, err);
---
>          
  fprintf(stderr, "WaitForMultipleObjects error %d %d\n",
ret, err);
==================================

Ely Soto

Ely Soto <address@hidden>
Sent by: address@hidden

04/09/2007 01:54 PM

Please respond to
address@hidden

To	address@hidden
cc
Subject	Re: [Qemu-devel] 0.9.0 Win32 Tap inferface PPC Guest issue

Ok I located the source of the problem. 

The code in main_loop_wait()
that uses WaitForMultipleObjects
will only service one object that woke it up. 

What is occuring is that the host_alarm timer is being serviced anytime
the tap_semaphore is also signaled, therefore the tap callback function
is 
never called while at the same time the tap_semaphore count is decremented.
This guarantees that the callback function will never get services if that
particular timing continues. 

This is likely something that won't occur on every system because of the
nature of the timing, but it is a problem. 

I'm working on a better fix as right now my solution is to poll all the
objects after a wakeup to see who really is signaled.
In order to do that you must use an Event Object in Manual Reset Mode.

vl.c 

void main_loop_wait(int
timeout) 
... 
        WaitObjects *w = &wait_objects;
        
        ret = WaitForMultipleObjects(w->num, w->events,
FALSE, timeout); 
        if (WAIT_OBJECT_0 + 0 <= ret &&
ret <= WAIT_OBJECT_0 + w->num - 1) { 
            if (w->func[ret - WAIT_OBJECT_0])
                w->func[ret
- WAIT_OBJECT_0](w->opaque[ret - WAIT_OBJECT_0]);
        } else if (ret == WAIT_TIMEOUT) {
        } else { 
            err = GetLastError();
            fprintf(stderr, "Wait error
%d %d\n", ret, err); 
        } 
... 



Ely Soto

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