[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