Re: [Qemu-devel] [PATCH 09/26] ehci: Use uframe precision for interrupt threshold checking

[Gerd Hoffmann]

On 12/17/12 15:47, Hans de Goede wrote:
> Hi,
> 
> On 12/17/2012 03:39 PM, Gerd Hoffmann wrote:
>> On 12/17/12 15:23, Hans de Goede wrote:
>>> Hi,
>>>
>>> On 12/17/2012 02:16 PM, Gerd Hoffmann wrote:
>>>> On 12/14/12 14:35, Hans de Goede wrote:
>>>>> Note that a shadow variable is used instead of changing frindex to
>>>>> uframe accuracy because we must send a frindex which is a multiple
>>>>> of 8
>>>>> during migration for migration compatibility, and rounding it down to
>>>>> a multiple of 8 pre-migration, can lead to frindex going backwards
>>>>> from
>>>>> the guest pov.
>>>>
>>>> Jumping forward instead?
>>>
>>> You mean rounding the send frindex up pre-migration, I didn't really
>>> consider
>>> that as it will cause us skipping processing an entry in the periodic
>>> frame
>>> list. I guess doing that on migration isn't too bad. OTOH giving the
>>> guest
>>> only frame accuracy like we've been doing till now also works fine...
>>>
>>> Your choice :)
>>
>> I'm looking for a way to avoid the shadow variable, but of course
>> without breaking migration.  giving the guest only frame accuracy looks
>> good to me.
> 
> Ok, but then we need the shadow variable, iow then the patch stays as is
> ...

Can't we (a) switch frindex to microframe resolution, (b) round to frame
resolution in pre_save and (c) return frindex & ~7 on guest register reads?

cheers,
  Gerd