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RE: [Xen-devel] [PATCH] Append 'nohpet' in dom0 cmdline to prevent dom0 from using HPET

  • To: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
  • From: "Wei, Gang" <gang.wei@xxxxxxxxx>
  • Date: Thu, 15 Oct 2009 10:13:45 +0800
  • Accept-language: en-US
  • Acceptlanguage: en-US
  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
  • Delivery-date: Wed, 14 Oct 2009 19:15:59 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcpNCKaBrvPTCpZlRnyPo/xyul0pxgAKWEng
  • Thread-topic: [Xen-devel] [PATCH] Append 'nohpet' in dom0 cmdline to prevent dom0 from using HPET

Jeremy Fitzhardinge wrote:
> On 10/14/09 02:26, Wei, Gang wrote:
>> Append 'nohpet' in dom0 cmdline to prevent dom0 from using HPET
>> Xen is using HPET to wakeup cpu from deep c-states, so the HPET
>> usage in dom0 must be fobidden. In 2.6.18-xen, the HPET was by
>> default disabled in config file. For upstream kernel built for pv
>> dom0, it is not practical to disable dom0 HPET usage in that way
>> because the same image may be also using as bare metal kernerl. So
>> add cmdline option to do this thing for dom0. 
> I think it would be better to unstatic disable_hpet() and call it from
> Xen setup.  But as far as I can see hpet_init() should never be called
> under Xen, because pv_time_ops won't be pointing to it, so there won't
> be any attempt to use the hpet.

Call disable_hpet() in dom0 xen setup phase will disable physical hpet and 
break hpet usage in hypervisor. There are another path to initialize hpet: 
fs_initcall(hpet_late_init), hpet_late_init()->hpet_enable().


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