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

["Denis V. Lunev" <den@openvz.org>]

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 <v.maffione@gmail.com>
>      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 <den@openvz.org>
> CC: Vincenzo Maffione <v.maffione@gmail.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> ---
>   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