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

["Denis V. Lunev" <den-lists@xxxxxxxxxxxxx>]

On 09/15/2016 03:22 PM, Ed Swierk wrote:
> On Thu, Sep 15, 2016 at 2:15 AM, Denis V. Lunev <den@xxxxxxxxxx> wrote:
>> 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?
> How can I tell which interrupt is firing? Instrument the QEMU e1000 code?
>
> --Ed
>
connect with gdb to qemu, set break into set_interrupt_cause
and dump value of  s->mac_reg[ICS], s->mac_reg[IMS] and s->mac_reg[ICR]

Bits are defined here hw/net/e1000_regs.h

/* Interrupt Cause Read */
#define E1000_ICR_TXDW          0x00000001 /* Transmit desc written back */
#define E1000_ICR_TXQE          0x00000002 /* Transmit Queue empty */

Den

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