[Qemu-devel] [PATCH v4 0/6] prevent QEMU from waking up needlessly

[Qemu-devel] [PATCH v4 0/6] 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 fixes win32_rearm_timer and mm_rearm_timer that
risk an overflow if INT64_MAX is passed as delta.

The fifth 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.



Changes in v4:

- do not initialize pcspk on xen;

- disable rtc_clock only when it points to the host_clock (the default);

- make sure it compiles on older xen versions.


Changes in v3:

- added a new patch to fix win32_rearm_timer and mm_rearm_timer, that
risk an overflow if INT64_MAX is passed as delta.



Shortlog and diffstat follow:

Stefano Stabellini (6):
      xen: do not initialize the interval timer and PCSPK emulator
      xen: disable rtc_clock
      xen: introduce an event channel for buffered io event notifications
      timers: the rearm function should be able to handle delta = INT64_MAX
      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      |    9 ++++++---
 qemu-timer.c |   30 ++++++++++++++++++------------
 xen-all.c    |   49 +++++++++++++++++++++++++++++++++++++++++++------
 3 files changed, 67 insertions(+), 21 deletions(-)


A git tree, based on fd39941ac78fbe969e292eeb91415ec548bd97a6, is available here:

git://xenbits.xen.org/people/sstabellini/qemu-dm.git timers-4

Cheers,

Stefano

[Qemu-devel] [PATCH v4 1/6] xen: do not initialize the interval timer and PCSPK emulator

[Stefano Stabellini]

PIT and PCSPK are emulated by the hypervisor so we don't need to emulate
them 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 |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/hw/pc.c b/hw/pc.c
index 31608d3..18abee0 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -44,6 +44,7 @@
 #include "ui/qemu-spice.h"
 #include "memory.h"
 #include "exec-memory.h"
+#include "arch_init.h"
 
 /* output Bochs bios info messages */
 //#define DEBUG_BIOS
@@ -1137,7 +1138,7 @@ 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);
@@ -1158,8 +1159,10 @@ 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);
-    pcspk_init(pit);
+    if (!xen_available()) {
+        pit = pit_init(isa_bus, 0x40, 0);
+        pcspk_init(pit);
+    }
 
     for(i = 0; i < MAX_SERIAL_PORTS; i++) {
         if (serial_hds[i]) {
-- 
1.7.2.5

[Qemu-devel] [PATCH v4 2/6] 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 |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/xen-all.c b/xen-all.c
index fd39168..101c962 100644
--- a/xen-all.c
+++ b/xen-all.c
@@ -514,6 +514,10 @@ void xen_vcpu_init(void)
         qemu_register_reset(xen_reset_vcpu, first_cpu);
         xen_reset_vcpu(first_cpu);
     }
+    /* if rtc_clock is left to default (host_clock), disable it */
+    if (rtc_clock == host_clock) {
+        qemu_clock_enable(rtc_clock, false);
+    }
 }
 
 /* get the ioreq packets from share mem */
-- 
1.7.2.5

[Qemu-devel] [PATCH v4 3/6] 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 |   45 +++++++++++++++++++++++++++++++++++++++------
 1 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/xen-all.c b/xen-all.c
index 101c962..0ce8002 100644
--- a/xen-all.c
+++ b/xen-all.c
@@ -59,6 +59,9 @@ static inline ioreq_t *xen_vcpu_ioreq(shared_iopage_t *shared_page, int vcpu)
 }
 #  define FMT_ioreq_size "u"
 #endif
+#ifndef HVM_PARAM_BUFIOREQ_EVTCHN
+#define HVM_PARAM_BUFIOREQ_EVTCHN 26
+#endif
 
 #define BUFFER_IO_MAX_DELAY  100
 
@@ -77,6 +80,8 @@ 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 */
@@ -549,6 +554,12 @@ 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) {
@@ -697,16 +708,18 @@ 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];
@@ -731,15 +744,21 @@ 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)
@@ -869,7 +888,6 @@ 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);
@@ -921,6 +939,7 @@ int xen_hvm_init(void)
 {
     int i, rc;
     unsigned long ioreq_pfn;
+    unsigned long bufioreq_evtchn;
     XenIOState *state;
 
     state = g_malloc0(sizeof (XenIOState));
@@ -970,6 +989,20 @@ 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 v4 4/6] timers: the rearm function should be able to handle delta = INT64_MAX

[Stefano Stabellini]

Fix win32_rearm_timer and mm_rearm_timer: they should be able to handle
INT64_MAX as a delta parameter without overflowing.
Also, the next deadline in ms should be calculated rounding down rather
than up (see unix_rearm_timer and dynticks_rearm_timer).

Finally ChangeTimerQueueTimer takes an unsigned long and timeSetEvent
takes an unsigned int as delta, so cast the ms delta to the appropriate
unsigned integer.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 qemu-timer.c |   18 +++++++++++++-----
 1 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/qemu-timer.c b/qemu-timer.c
index a22f27e..29410f1 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -696,13 +696,17 @@ static void mm_stop_timer(struct qemu_alarm_timer *t)
 
 static void mm_rearm_timer(struct qemu_alarm_timer *t, int64_t delta)
 {
-    int nearest_delta_ms = (delta + 999999) / 1000000;
+    int64_t nearest_delta_ms = delta / 1000000;
     if (nearest_delta_ms < 1) {
         nearest_delta_ms = 1;
     }
+    /* UINT_MAX can be 32 bit */
+    if (nearest_delta_ms > UINT_MAX) {
+        nearest_delta_ms = UINT_MAX;
+    }
 
     timeKillEvent(mm_timer);
-    mm_timer = timeSetEvent(nearest_delta_ms,
+    mm_timer = timeSetEvent((unsigned int) nearest_delta_ms,
                             mm_period,
                             mm_alarm_handler,
                             (DWORD_PTR)t,
@@ -757,16 +761,20 @@ static void win32_rearm_timer(struct qemu_alarm_timer *t,
                               int64_t nearest_delta_ns)
 {
     HANDLE hTimer = t->timer;
-    int nearest_delta_ms;
+    int64_t nearest_delta_ms;
     BOOLEAN success;
 
-    nearest_delta_ms = (nearest_delta_ns + 999999) / 1000000;
+    nearest_delta_ms = nearest_delta_ns / 1000000;
     if (nearest_delta_ms < 1) {
         nearest_delta_ms = 1;
     }
+    /* ULONG_MAX can be 32 bit */
+    if (nearest_delta_ms > ULONG_MAX) {
+        nearest_delta_ms = ULONG_MAX;
+    }
     success = ChangeTimerQueueTimer(NULL,
                                     hTimer,
-                                    nearest_delta_ms,
+                                    (unsigned long) nearest_delta_ms,
                                     3600000);
 
     if (!success) {
-- 
1.7.2.5

[Qemu-devel] [PATCH v4 5/6] 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 29410f1..de20852 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

[Qemu-devel] [PATCH v4 6/6] 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 de20852..84b970e 100644
--- a/qemu-timer.c
+++ b/qemu-timer.c
@@ -823,6 +823,6 @@ fail:
 
 int qemu_calculate_timeout(void)
 {
-    return 1000;
+    return 1000*60*60;
 }
 
-- 
1.7.2.5