Re: [Xen-devel] [PATCH] Remove a set operation for VCPU_KICK_SOFTIRQ when post interrupt to vm.

["Zhang, Yang Z" <yang.z.zhang@xxxxxxxxx>]

Hanweidong (Randy) wrote on 2015-09-08:
> 
> Jan Beulich wrote on ent: 2015年9月7日 22:46:
>> Subject: Re: [Xen-devel] [PATCH] Remove a set operation for
>> VCPU_KICK_SOFTIRQ when post interrupt to vm.
>> 
>>>>> On 07.09.15 at 16:24, <john.liuqiming@xxxxxxxxxx> wrote:
>>> I believe this also has something to do with a windows guest boot hang
>>> issue.
>>> 
>>> It randomly occured, when boot a guest has windows 2008 os and pv-
>>> driver installed. The boot process hangs when wait xenstored replay
>>> event signal.
>>> 
>>> It can be reproduced after hundreds reboot using the xen staging
>>> branch. But after I changed this code the hang issue can not reproduce.
>> 
>> The change below (which I don't think was ever posted to xen-devel)
>> does not make any sense, as it prohibits timely delivery of guest
>> interrupts. If there is an issue, I think you'd need to start with
>> clearly
> 
> This change won't prohibit timely delivery of guest interrupts,
> intead, it helps to deliver guest interrupt timely. Posted interrupt
> delivery doesn't kick cpu, so it should not set VCPU_KICK_SOFTIRQ bit,
> and doesn't care about if VCPU_KICK_SOFTIRQ is set or not. if
> VCPU_KICK_SOFTIRQ is set, next interrupt will not be delivered due to
> test_and_set_bit check. What's more, it also impacts vcpu_kick() to
> kick cpu (smp_send_event_check_cpu) when VCPU_KICK_SOFTIRQ is set.

The patch seems wrong to me since the interrupt will lost in some corner cases 
with those changes. Can you explain more detail like why next interrupt will 
get lost if set the softirq here?

Best regards,
Yang


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