Re: [Qemu-devel] EHCI USB regression in 1.2.0 - ehci_state_fetchqtd() asserting

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 10/08/2012 10:18 PM, Shawn Starr wrote:
> On Monday, October 08, 2012 10:10:49 PM Hans de Goede wrote:
>> Hi,
>>
>> On 10/08/2012 06:11 PM, Johannes Stezenbach wrote:
>>
>> <mega snip>
>>
>>   > I also wonder if this is not a generic problem
>>>
>>> for all emulated hw if the driver uses some timeout?
>>
>> Yes it likely is, because the emulated timer interrupt will
>> try to make up for time lost when the vm was not running
>> (in either hypervisor or guest mode), while as hw emulation
>> code which has been pre-empted for what ever reason my
>> simply need some more actual running time before it can
>> complete the task as hand, at which point the timeout
>> will trigger sooner then the hw emulation can handle the
>> task ...
>>
>> Note that with the EHCI emulation we also can have the
>> 2 (guest and hw-emulation time) get out of sync in the
>> other way. When we got behind in processing frames
>> on the periodic schedule compared to "real-time" we would
>> catch up too fast, causing the guest to see large
>> jumps in the frindex register, which it does not like.
>>
>> So all of this really is a precarious balancing act, and
>> to get back to the subject of the thread, the latency
>> spikes some of the kernels debugging options can cause,
>> can upset the balance...
>>
>
> Hello folks,
>
> I am using a non-debug kernel (because debug kernels are seriously sluggish).
> I may elect to get kernel-3.6.0-3.fc18 or  kernel-3.6.1-1.fc18 from koji also
> since 3.6 is final now.
>
> Currently using: 3.6.0-0.rc7.git0.1.fc18.x86_64

Hmm, so were you using this at the time you hit the bug you reported
earlier too ? And can you reproduce that bug or was it a one
time occurence ?

Regards,

Hans