Re: [Qemu-devel] [PATCH for 2.5 1/1] e1000: fix hang of win2k12 shutdown with flood ping

[Jason Wang]

On 11/27/2015 07:42 PM, Denis V. Lunev wrote:
> On 11/27/2015 09:50 AM, Denis V. Lunev wrote:
>> On 11/27/2015 09:48 AM, Denis V. Lunev wrote:
>>> e1000 driver in Win2k12 is really well rotten. It 100% hangs on
>>> shutdown
>>> of UP VM under flood ping. The guest checks card state and reinjects
>>> itself interrupt in a loop. This is fatal for UP machine.
>>>
>>> There is no good way to fix this misbehavior but to kludge it. The
>>> emulation has interrupt throttling register aka ITR which limits
>>> interrupt rate and allows the guest to proceed this phase.
>>> There is no problem with this kludge for Linux guests - it adjust the
>>> value of it itself.
>>>
>>> On the other hand according to the initial research in
>>>      commit e9845f0985f088dd01790f4821026df0afba5795
>>>      Author: Vincenzo Maffione <address@hidden>
>>>      Date:   Fri Aug 2 18:30:52 2013 +0200
>>>
>>>      e1000: add interrupt mitigation support
>>>
>>>      ...
>>>
>>>      Interrupt mitigation boosts performance when the guest suffers
>>> from
>>>      an high interrupt rate (i.e. receiving short UDP packets at
>>> high packet
>>>      rate). For some numerical results see the following link
>>> http://info.iet.unipi.it/~luigi/papers/20130520-rizzo-vm.pdf
>>>
>>> this should also boost performance a bit.
>>>
>>> See https://bugzilla.redhat.com/show_bug.cgi?id=874406 for additional
>>> details.
>>>
>>> Signed-off-by: Denis V. Lunev <address@hidden>
>>> CC: Vincenzo Maffione <address@hidden>
>>> CC: Stefan Hajnoczi <address@hidden>
>>> ---
>>>   hw/net/e1000.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/hw/net/e1000.c b/hw/net/e1000.c
>>> index c877e06..0af528f 100644
>>> --- a/hw/net/e1000.c
>>> +++ b/hw/net/e1000.c
>>> @@ -447,6 +447,9 @@ static void e1000_reset(void *opaque)
>>>           e1000_link_down(d);
>>>       }
>>>   +    /* Throttle interrupts to allow poor Win 2012 to shutdown */
>>> +    d->mac_reg[ITR] = 250;
>>> +
>>>       /* Some guests expect pre-initialized RAH/RAL (AddrValid flag
>>> + MACaddr) */
>>>       d->mac_reg[RA] = 0;
>>>       d->mac_reg[RA + 1] = E1000_RAH_AV;
>> Intel manual says about ITR that " A initial suggested range is
>> 651-5580 (28Bh - 15CCh)."
>> Should we use something other than 250? :)
>>
>> http://www.intel.com/content/www/us/en/embedded/products/networking/pci-pci-x-family-gbe-controllers-software-dev-manual.html
>>
>>
>> Den
>
> Jason, can you look to this?
>
> I have rechecked MAINTAINERs file and found that
> I have missed you here. Sorry :(
>
> Den
>

No problem.

But I have a question. What if ITR is disabled?