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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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
describing the issue you see and what you think it is being caused by.

Jan

> On 2015/9/7 22:46, - wrote:
>> From: liuqiming 00178499 <john.liuqiming@xxxxxxxxxx>
>>
>> This set operation doesn't make any sense, and it will block later
>> interrupt injected into vm (by vcpu_kick or deliver_posted_intr),
>> which will cause a performance issue on CPU supporting posted-interrupt.
>>
>> Signed-off-by: Qiming Liu <john.liuqiming@xxxxxxxxxx>
>> Cc: Yang Zhang <yang.z.zhang@xxxxxxxxx>
>> ---
>>   xen/arch/x86/hvm/vmx/vmx.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>> index 2582cdd..9480b44 100644
>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>> @@ -1681,7 +1681,7 @@ static void __vmx_deliver_posted_interrupt(struct vcpu 
> *v)
>>       {
>>           unsigned int cpu = v->processor;
>>   
>> -        if ( !test_and_set_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu))
>> +        if ( !test_bit(VCPU_KICK_SOFTIRQ, &softirq_pending(cpu))
>>                && (cpu != smp_processor_id()) )
>>               send_IPI_mask(cpumask_of(cpu), posted_intr_vector);
>>       }
> 
> 
> 
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