Re: [Qemu-devel] [Xen-devel] [RFC] e1000: Don't save writes to ICS/ICR masked by IMS

[Denis V. Lunev]

On 09/13/2016 11:59 PM, Konrad Rzeszutek Wilk wrote:
> On Thu, Sep 01, 2016 at 10:57:48AM -0700, Ed Swierk wrote:
>> Windows 8, 10 and Server 2012 guests hang intermittently while booting
>> on Xen 4.5.3 with 1 vCPU and 4 e1000 vNICs, shortly after the Windows
>> logo appears and the little dots start spinning.
>>
>> Running strace on qemu shows its main thread doing the following every
>> couple of milliseconds:
>>
>>  ppoll([..., {fd=30</dev/xen/evtchn>, events=POLLIN|POLLERR|POLLHUP},
>>         ...], ...) = 1 ([{fd=30, revents=POLLIN}], ...)
>>  read(30</dev/xen/evtchn>, "^\0\0\0", 4) = 4
>>  write(30</dev/xen/evtchn>, "^\0\0\0", 4) = 4
>>  ioctl(30</dev/xen/evtchn>, IOCTL_EVTCHN_NOTIFY, 0x7f1f9449d310) = 0
>>  clock_gettime(CLOCK_MONOTONIC, {6937, 449468262}) = 0
>>  clock_gettime(CLOCK_MONOTONIC, {6937, 449582903}) = 0
>>  gettimeofday({1472251376, 673434}, NULL) = 0
>>  clock_gettime(CLOCK_MONOTONIC, {6937, 449856205}) = 0
>>  gettimeofday({1472251376, 673679}, NULL) = 0
>>
>> The event channel (identified by '^' or 94 in this example) is always
>> the third of the domain's four channels.
>>
>> Two recent qemu patches (http://git.qemu.org/?p=qemu.git;h=9596ef7c and
>> http://git.qemu.org/?p=qemu.git;h=74004e8c) seem to address similar
>> issues, but don't help in this case.
>>
>> The proposed fix from
>> https://bugzilla.redhat.com/show_bug.cgi?id=874406#c78 makes the hang
>> go away. It's not clear to me why it works, or if it's just papering
>> over a bug elsewhere, or if there are any possible side effects.
> CC-ing Denis.
>
>
> Is the fix below based on reading the spec or more of instrumenting?
>
> Thanks.

hmm. I have looked in our older code (completely separate
from QEMU). It does not have this trick.

2012r2 (as far as I remember) has a bug in the driver
when LSC interrupt was raised unexpectedly during driver
initialization. The original bug was about TXQE. Can you
pls confirm which interrupt causes the storm?

Den