[Qemu-devel] [PATCH v2 0/5] prevent Qemu from waking up needlessly

[Qemu-devel] [PATCH v2 0/5] prevent Qemu from waking up needlessly

[Stefano Stabellini]

Hi all,
this small patch series prevents Qemu from waking up needlessly on Xen
several times a second in order to check some timers.


The first patch stops Qemu from emulating the PIT on Xen, the second
patch disables the rtc_clock entirely.

The third patch makes use of a new mechanism to receive buffered io
event notifications from Xen, so that Qemu doesn't need to check the
buffered io page for data 10 times a sec for the entire life of the VM.

The fourth patch changes qemu_next_alarm_deadline only to check the
expire time of a clock if it is enabled.

Finally the last patch increases the default select timeout to 1h:
nothing should rely on the select timeout to be 1sec, so we might as
well increase it to 1h.



Shortlog and diffstat follow:

Stefano Stabellini (5):
      xen: do not initialize the interval timer emulator
      xen: disable rtc_clock
      xen: introduce an event channel for buffered io event notifications
      qemu_next_alarm_deadline: check the expire time of a clock only if it is enabled
      qemu_calculate_timeout: increase minimum timeout to 1h

 hw/pc.c      |    7 +++++--
 qemu-timer.c |   12 +++++-------
 xen-all.c    |   43 +++++++++++++++++++++++++++++++++++++------
 3 files changed, 47 insertions(+), 15 deletions(-)


A git tree available here:

git://xenbits.xen.org/people/sstabellini/qemu-dm.git timers-2

Cheers,

Stefano

[Qemu-devel] [PATCH v2 1/5] xen: do not initialize the interval timer emulator

[Stefano Stabellini]

PIT is emulated by the hypervisor so we don't need to emulate it in Qemu:
this patch prevents Qemu from waking up needlessly at PIT_FREQ on Xen.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 hw/pc.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/pc.c b/hw/pc.c
index 85304cf..7a7ce98 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -43,6 +43,7 @@
 #include "ui/qemu-spice.h"
 #include "memory.h"
 #include "exec-memory.h"
+#include "arch_init.h"
 
 /* output Bochs bios info messages */
 //#define DEBUG_BIOS
@@ -1130,7 +1131,7 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
     DriveInfo *fd[MAX_FD];
     qemu_irq rtc_irq = NULL;
     qemu_irq *a20_line;
-    ISADevice *i8042, *port92, *vmmouse, *pit;
+    ISADevice *i8042, *port92, *vmmouse, *pit = NULL;
     qemu_irq *cpu_exit_irq;
 
     register_ioport_write(0x80, 1, 1, ioport80_write, NULL);
@@ -1151,7 +1152,9 @@ void pc_basic_device_init(ISABus *isa_bus, qemu_irq *gsi,
 
     qemu_register_boot_set(pc_boot_set, *rtc_state);
 
-    pit = pit_init(isa_bus, 0x40, 0);
+    if (!xen_available()) {
+        pit = pit_init(isa_bus, 0x40, 0);
+    }
     pcspk_init(pit);
 
     for(i = 0; i < MAX_SERIAL_PORTS; i++) {
-- 
1.7.2.5

[Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Stefano Stabellini]

rtc_clock is only used by the RTC emulator (mc146818rtc.c), however Xen
has its own RTC emulator in the hypervisor so we can disable it.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 xen-all.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/xen-all.c b/xen-all.c
index d1fc597..bf183f7 100644
--- a/xen-all.c
+++ b/xen-all.c
@@ -513,6 +513,7 @@ void xen_vcpu_init(void)
         qemu_register_reset(xen_reset_vcpu, first_cpu);
         xen_reset_vcpu(first_cpu);
     }
+    qemu_clock_enable(rtc_clock, false);
 }
 
 /* get the ioreq packets from share mem */
-- 
1.7.2.5

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Paolo Bonzini]

On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> rtc_clock is only used by the RTC emulator (mc146818rtc.c), however Xen
> has its own RTC emulator in the hypervisor so we can disable it.
>
> Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> ---
>   xen-all.c |    1 +
>   1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/xen-all.c b/xen-all.c
> index d1fc597..bf183f7 100644
> --- a/xen-all.c
> +++ b/xen-all.c
> @@ -513,6 +513,7 @@ void xen_vcpu_init(void)
>           qemu_register_reset(xen_reset_vcpu, first_cpu);
>           xen_reset_vcpu(first_cpu);
>       }
> +    qemu_clock_enable(rtc_clock, false);
>   }
>
>   /* get the ioreq packets from share mem */

Depending on "-rtc clock=vm" or "-rtc clock=rt", this may not be true.

Why do you need to instantiate an RTC at all?

Paolo

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Stefano Stabellini]

On Fri, 27 Jan 2012, Paolo Bonzini wrote:
> On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> > rtc_clock is only used by the RTC emulator (mc146818rtc.c), however Xen
> > has its own RTC emulator in the hypervisor so we can disable it.
> >
> > Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> > ---
> >   xen-all.c |    1 +
> >   1 files changed, 1 insertions(+), 0 deletions(-)
> >
> > diff --git a/xen-all.c b/xen-all.c
> > index d1fc597..bf183f7 100644
> > --- a/xen-all.c
> > +++ b/xen-all.c
> > @@ -513,6 +513,7 @@ void xen_vcpu_init(void)
> >           qemu_register_reset(xen_reset_vcpu, first_cpu);
> >           xen_reset_vcpu(first_cpu);
> >       }
> > +    qemu_clock_enable(rtc_clock, false);
> >   }
> >
> >   /* get the ioreq packets from share mem */
> 
> Depending on "-rtc clock=vm" or "-rtc clock=rt", this may not be true.

Good point.
I should check for rtc_clock == host_clock.


> Why do you need to instantiate an RTC at all?

I don't, in fact in previous versions of this patch series I tried to do
that but it is difficult and makes the common code worse, so I followed
Anthony's suggestion of just disabling the rtc_clock.

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Paolo Bonzini]

On 01/30/2012 12:56 PM, Stefano Stabellini wrote:
>> >  Depending on "-rtc clock=vm" or "-rtc clock=rt", this may not be true.
>
> Good point.
> I should check for rtc_clock == host_clock.
>
>> >  Why do you need to instantiate an RTC at all?
> I don't, in fact in previous versions of this patch series I tried to do
> that but it is difficult and makes the common code worse, so I followed
> Anthony's suggestion of just disabling the rtc_clock.

I see.  It shouldn't surprise you that I completely disagree with 
Anthony on this. :)

Paolo

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Stefano Stabellini]

On Mon, 30 Jan 2012, Paolo Bonzini wrote:
> On 01/30/2012 12:56 PM, Stefano Stabellini wrote:
> >> >  Depending on "-rtc clock=vm" or "-rtc clock=rt", this may not be true.
> >
> > Good point.
> > I should check for rtc_clock == host_clock.
> >
> >> >  Why do you need to instantiate an RTC at all?
> > I don't, in fact in previous versions of this patch series I tried to do
> > that but it is difficult and makes the common code worse, so I followed
> > Anthony's suggestion of just disabling the rtc_clock.
> 
> I see.  It shouldn't surprise you that I completely disagree with 
> Anthony on this. :)

I am OK with both approaches, but I can see the benefits of reducing
this patch to (almost) a one-liner.

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Anthony Liguori]

On 01/30/2012 05:59 AM, Paolo Bonzini wrote:
> On 01/30/2012 12:56 PM, Stefano Stabellini wrote:
>>> > Depending on "-rtc clock=vm" or "-rtc clock=rt", this may not be true.
>>
>> Good point.
>> I should check for rtc_clock == host_clock.
>>
>>> > Why do you need to instantiate an RTC at all?
>> I don't, in fact in previous versions of this patch series I tried to do
>> that but it is difficult and makes the common code worse, so I followed
>> Anthony's suggestion of just disabling the rtc_clock.
>
> I see. It shouldn't surprise you that I completely disagree with Anthony on
> this. :)

Give me some credit at least...

The original patches didn't disable the RTC, it introduced a half-neutered Xen 
specific RTC.

My original suggestion (which I still think is the best approach) is to change 
the RTC emulation to not use a second timer at all.

Regards,

Anthony Liguori

> Paolo
>

Re: [Qemu-devel] [PATCH v2 2/5] xen: disable rtc_clock

[Paolo Bonzini]

On 01/30/2012 08:28 PM, Anthony Liguori wrote:
>>
>> I see. It shouldn't surprise you that I completely disagree with
>> Anthony on this. :)
>
> Give me some credit at least...
>
> The original patches didn't disable the RTC, it introduced a
> half-neutered Xen specific RTC.

Ah. :)

> My original suggestion (which I still think is the best approach) is to
> change the RTC emulation to not use a second timer at all.

Yes, that would be really the best approach.  I tried and it's pretty 
hard, but we can give it a second try.

Paolo

[Qemu-devel] [PATCH v2 3/5] xen: introduce an event channel for buffered io event notifications

[Stefano Stabellini]

Use the newly introduced HVM_PARAM_BUFIOREQ_EVTCHN to receive
notifications for buffered io events.
After the first notification is received leave the event channel masked
and setup a timer to process the rest of the batch.
Once we have completed processing the batch, unmask the event channel
and delete the timer.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 xen-all.c |   42 ++++++++++++++++++++++++++++++++++++------
 1 files changed, 36 insertions(+), 6 deletions(-)

diff --git a/xen-all.c b/xen-all.c
index bf183f7..bfec4c1 100644
--- a/xen-all.c
+++ b/xen-all.c
@@ -77,6 +77,8 @@ typedef struct XenIOState {
     QEMUTimer *buffered_io_timer;
     /* the evtchn port for polling the notification, */
     evtchn_port_t *ioreq_local_port;
+    /* evtchn local port for buffered io */
+    evtchn_port_t bufioreq_local_port;
     /* the evtchn fd for polling */
     XenEvtchn xce_handle;
     /* which vcpu we are serving */
@@ -545,6 +547,12 @@ static ioreq_t *cpu_get_ioreq(XenIOState *state)
     evtchn_port_t port;
 
     port = xc_evtchn_pending(state->xce_handle);
+    if (port == state->bufioreq_local_port) {
+        qemu_mod_timer(state->buffered_io_timer,
+                BUFFER_IO_MAX_DELAY + qemu_get_clock_ms(rt_clock));
+        return NULL;
+    }
+
     if (port != -1) {
         for (i = 0; i < smp_cpus; i++) {
             if (state->ioreq_local_port[i] == port) {
@@ -693,16 +701,18 @@ static void handle_ioreq(ioreq_t *req)
     }
 }
 
-static void handle_buffered_iopage(XenIOState *state)
+static int handle_buffered_iopage(XenIOState *state)
 {
     buf_ioreq_t *buf_req = NULL;
     ioreq_t req;
     int qw;
 
     if (!state->buffered_io_page) {
-        return;
+        return 0;
     }
 
+    memset(&req, 0x00, sizeof(req));
+
     while (state->buffered_io_page->read_pointer != state->buffered_io_page->write_pointer) {
         buf_req = &state->buffered_io_page->buf_ioreq[
             state->buffered_io_page->read_pointer % IOREQ_BUFFER_SLOT_NUM];
@@ -727,15 +737,21 @@ static void handle_buffered_iopage(XenIOState *state)
         xen_mb();
         state->buffered_io_page->read_pointer += qw ? 2 : 1;
     }
+
+    return req.count;
 }
 
 static void handle_buffered_io(void *opaque)
 {
     XenIOState *state = opaque;
 
-    handle_buffered_iopage(state);
-    qemu_mod_timer(state->buffered_io_timer,
-                   BUFFER_IO_MAX_DELAY + qemu_get_clock_ms(rt_clock));
+    if (handle_buffered_iopage(state)) {
+        qemu_mod_timer(state->buffered_io_timer,
+                BUFFER_IO_MAX_DELAY + qemu_get_clock_ms(rt_clock));
+    } else {
+        qemu_del_timer(state->buffered_io_timer);
+        xc_evtchn_unmask(state->xce_handle, state->bufioreq_local_port);
+    }
 }
 
 static void cpu_handle_ioreq(void *opaque)
@@ -865,7 +881,6 @@ static void xen_main_loop_prepare(XenIOState *state)
 
     state->buffered_io_timer = qemu_new_timer_ms(rt_clock, handle_buffered_io,
                                                  state);
-    qemu_mod_timer(state->buffered_io_timer, qemu_get_clock_ms(rt_clock));
 
     if (evtchn_fd != -1) {
         qemu_set_fd_handler(evtchn_fd, cpu_handle_ioreq, NULL, state);
@@ -917,6 +932,7 @@ int xen_hvm_init(void)
 {
     int i, rc;
     unsigned long ioreq_pfn;
+    unsigned long bufioreq_evtchn;
     XenIOState *state;
 
     state = g_malloc0(sizeof (XenIOState));
@@ -966,6 +982,20 @@ int xen_hvm_init(void)
         state->ioreq_local_port[i] = rc;
     }
 
+    rc = xc_get_hvm_param(xen_xc, xen_domid, HVM_PARAM_BUFIOREQ_EVTCHN,
+            &bufioreq_evtchn);
+    if (rc < 0) {
+        fprintf(stderr, "failed to get HVM_PARAM_BUFIOREQ_EVTCHN\n");
+        return -1;
+    }
+    rc = xc_evtchn_bind_interdomain(state->xce_handle, xen_domid,
+            (uint32_t)bufioreq_evtchn);
+    if (rc == -1) {
+        fprintf(stderr, "bind interdomain ioctl error %d\n", errno);
+        return -1;
+    }
+    state->bufioreq_local_port = rc;
+
     /* Init RAM management */
     xen_map_cache_init();
     xen_ram_init(ram_size);
-- 
1.7.2.5

[Qemu-devel] [PATCH v2 4/5] qemu_next_alarm_deadline: check the expire time of a clock only if it is enabled

[Stefano Stabellini]

Also delta in qemu_next_alarm_deadline is a 64 bit value so set the
default to INT64_MAX instead of INT32_MAX.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 qemu-timer.c |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/qemu-timer.c b/qemu-timer.c
index cd026c6..648db1d 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -106,23 +106,21 @@ static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
 
 static int64_t qemu_next_alarm_deadline(void)
 {
-    int64_t delta;
+    int64_t delta = INT64_MAX;
     int64_t rtdelta;
 
-    if (!use_icount && vm_clock->active_timers) {
+    if (!use_icount && vm_clock->enabled && vm_clock->active_timers) {
         delta = vm_clock->active_timers->expire_time -
                      qemu_get_clock_ns(vm_clock);
-    } else {
-        delta = INT32_MAX;
     }
-    if (host_clock->active_timers) {
+    if (host_clock->enabled && host_clock->active_timers) {
         int64_t hdelta = host_clock->active_timers->expire_time -
                  qemu_get_clock_ns(host_clock);
         if (hdelta < delta) {
             delta = hdelta;
         }
     }
-    if (rt_clock->active_timers) {
+    if (rt_clock->enabled && rt_clock->active_timers) {
         rtdelta = (rt_clock->active_timers->expire_time -
                  qemu_get_clock_ns(rt_clock));
         if (rtdelta < delta) {
-- 
1.7.2.5

Re: [Qemu-devel] [PATCH v2 4/5] qemu_next_alarm_deadline: check the expire time of a clock only if it is enabled

[Paolo Bonzini]

On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> Also delta in qemu_next_alarm_deadline is a 64 bit value so set the
> default to INT64_MAX instead of INT32_MAX.
>
> Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> ---
>   qemu-timer.c |   10 ++++------
>   1 files changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index cd026c6..648db1d 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -106,23 +106,21 @@ static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
>
>   static int64_t qemu_next_alarm_deadline(void)
>   {
> -    int64_t delta;
> +    int64_t delta = INT64_MAX;

I'm worried of overflows elsewhere...

>       int64_t rtdelta;
>
> -    if (!use_icount&&  vm_clock->active_timers) {
> +    if (!use_icount&&  vm_clock->enabled&&  vm_clock->active_timers) {
>           delta = vm_clock->active_timers->expire_time -
>                        qemu_get_clock_ns(vm_clock);
> -    } else {
> -        delta = INT32_MAX;
>       }
> -    if (host_clock->active_timers) {
> +    if (host_clock->enabled&&  host_clock->active_timers) {
>           int64_t hdelta = host_clock->active_timers->expire_time -
>                    qemu_get_clock_ns(host_clock);
>           if (hdelta<  delta) {
>               delta = hdelta;
>           }
>       }
> -    if (rt_clock->active_timers) {
> +    if (rt_clock->enabled&&  rt_clock->active_timers) {
>           rtdelta = (rt_clock->active_timers->expire_time -
>                    qemu_get_clock_ns(rt_clock));
>           if (rtdelta<  delta) {

The patch is otherwise okay, but without looking more closely at the 
callers I'm not quite ready to give my Reviewed-by.

Paolo

Re: [Qemu-devel] [PATCH v2 4/5] qemu_next_alarm_deadline: check the expire time of a clock only if it is enabled

[Stefano Stabellini]

On Fri, 27 Jan 2012, Paolo Bonzini wrote:
> On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> > Also delta in qemu_next_alarm_deadline is a 64 bit value so set the
> > default to INT64_MAX instead of INT32_MAX.
> >
> > Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> > ---
> >   qemu-timer.c |   10 ++++------
> >   1 files changed, 4 insertions(+), 6 deletions(-)
> >
> > diff --git a/qemu-timer.c b/qemu-timer.c
> > index cd026c6..648db1d 100644
> > --- a/qemu-timer.c
> > +++ b/qemu-timer.c
> > @@ -106,23 +106,21 @@ static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
> >
> >   static int64_t qemu_next_alarm_deadline(void)
> >   {
> > -    int64_t delta;
> > +    int64_t delta = INT64_MAX;
> 
> I'm worried of overflows elsewhere...

I think that you are right: mm_rearm_timer and win32_rearm_timer would
overflow.
I'll just repost the patch using INT32_MAX.

Re: [Qemu-devel] [PATCH v2 4/5] qemu_next_alarm_deadline: check the expire time of a clock only if it is enabled

[Stefano Stabellini]

On Fri, 27 Jan 2012, Stefano Stabellini wrote:
> On Fri, 27 Jan 2012, Paolo Bonzini wrote:
> > On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> > > Also delta in qemu_next_alarm_deadline is a 64 bit value so set the
> > > default to INT64_MAX instead of INT32_MAX.
> > >
> > > Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> > > ---
> > >   qemu-timer.c |   10 ++++------
> > >   1 files changed, 4 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/qemu-timer.c b/qemu-timer.c
> > > index cd026c6..648db1d 100644
> > > --- a/qemu-timer.c
> > > +++ b/qemu-timer.c
> > > @@ -106,23 +106,21 @@ static inline int alarm_has_dynticks(struct qemu_alarm_timer *t)
> > >
> > >   static int64_t qemu_next_alarm_deadline(void)
> > >   {
> > > -    int64_t delta;
> > > +    int64_t delta = INT64_MAX;
> > 
> > I'm worried of overflows elsewhere...
> 
> I think that you are right: mm_rearm_timer and win32_rearm_timer would
> overflow.
> I'll just repost the patch using INT32_MAX.
 
Actually it is better to fix mm_rearm_timer and win32_rearm_timer so
that they won't overflow anymore.
I'll add a patch to do that.

[Qemu-devel] [PATCH v2 5/5] qemu_calculate_timeout: increase minimum timeout to 1h

[Stefano Stabellini]

There is no reason why the minimum timeout should be 1sec, it could
easily be 1h and we would save lots of cpu cycles.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 qemu-timer.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/qemu-timer.c b/qemu-timer.c
index 648db1d..b792a32 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -844,6 +844,6 @@ fail:
 
 int qemu_calculate_timeout(void)
 {
-    return 1000;
+    return 1000*60*60;
 }
 
-- 
1.7.2.5

Re: [Qemu-devel] [PATCH v2 5/5] qemu_calculate_timeout: increase minimum timeout to 1h

[Paolo Bonzini]

On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> There is no reason why the minimum timeout should be 1sec, it could
> easily be 1h and we would save lots of cpu cycles.
>
> Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> ---
>   qemu-timer.c |    2 +-
>   1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 648db1d..b792a32 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -844,6 +844,6 @@ fail:
>
>   int qemu_calculate_timeout(void)
>   {
> -    return 1000;
> +    return 1000*60*60;
>   }
>

This might break Windows networking, but I'm going to fix it before 1.1 
anyway.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Paolo

Re: [Qemu-devel] [PATCH v2 5/5] qemu_calculate_timeout: increase minimum timeout to 1h

[Stefano Stabellini]

On Fri, 27 Jan 2012, Paolo Bonzini wrote:
> On 01/27/2012 01:26 PM, Stefano Stabellini wrote:
> > There is no reason why the minimum timeout should be 1sec, it could
> > easily be 1h and we would save lots of cpu cycles.
> >
> > Signed-off-by: Stefano Stabellini<stefano.stabellini@eu.citrix.com>
> > ---
> >   qemu-timer.c |    2 +-
> >   1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/qemu-timer.c b/qemu-timer.c
> > index 648db1d..b792a32 100644
> > --- a/qemu-timer.c
> > +++ b/qemu-timer.c
> > @@ -844,6 +844,6 @@ fail:
> >
> >   int qemu_calculate_timeout(void)
> >   {
> > -    return 1000;
> > +    return 1000*60*60;
> >   }
> >
> 
> This might break Windows networking, but I'm going to fix it before 1.1 
> anyway.
> 
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
 
Thanks!