Re: [Xen-devel] [RFC Patch v3 03/18] don't zero out ioreq page

[Wen Congyang <wency@xxxxxxxxxxxxxx>]

At 09/05/2014 05:25 PM, Paul Durrant Write:
>> -----Original Message-----
>> From: Wen Congyang [mailto:wency@xxxxxxxxxxxxxx]
>> Sent: 05 September 2014 10:11
>> To: xen devel
>> Cc: Ian Jackson; Ian Campbell; Eddie Dong; Jiang Yunhong; Lai Jiangshan; Yang
>> Hongyang; Wen Congyang; Paul Durrant
>> Subject: [RFC Patch v3 03/18] don't zero out ioreq page
>>
>> ioreq page may contain some pending I/O requests, and we need to
>> handle the pending I/O req after migration.
>>
>> TODO:
>> 1. update qemu to handle the pending I/O req
>>
>> Signed-off-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
>> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
>> ---
>>  tools/libxc/xc_domain_restore.c | 3 +--
>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/tools/libxc/xc_domain_restore.c
>> b/tools/libxc/xc_domain_restore.c
>> index fb4ddfc..21a6177 100644
>> --- a/tools/libxc/xc_domain_restore.c
>> +++ b/tools/libxc/xc_domain_restore.c
>> @@ -2310,8 +2310,7 @@ int xc_domain_restore(xc_interface *xch, int io_fd,
>> uint32_t dom,
>>      }
>>
>>      /* These comms pages need to be zeroed at the start of day */
>> -    if ( xc_clear_domain_page(xch, dom, tailbuf.u.hvm.magicpfns[0]) ||
>> -         xc_clear_domain_page(xch, dom, tailbuf.u.hvm.magicpfns[1]) ||
>> +    if ( xc_clear_domain_page(xch, dom, tailbuf.u.hvm.magicpfns[1]) ||
>>           xc_clear_domain_page(xch, dom, tailbuf.u.hvm.magicpfns[2]) )
> 
> If we're not nuking pfn[0] then we probably shouldn't nuke pfn[1] either 
> (buffererd ioreq).
> 

IIRC, in my early test, if we clear pfn[1], secondary vm doesn't response(I use 
vnc connect to secondary vm).
But I test it again, secondary vm doesn't response even if we don't clear 
pfn[1]. I will clear pfn[1] in
the next version.


> Does qemu need any modification? I don't think it makes any assumptions about 
> the initial state of ioreqs so all you may have to do is make sure each vcpu 
> event channel is kicked on resume (which is harmless even if there's no 
> pending ioreq... qemu will just ignore it and wait again).

Do you mean hypervisor kickes each vcpu event channel on resume? I will try it.

Thanks
Wen Congyang

> 
>   Paul
> 
>>      {
>>          PERROR("error zeroing magic pages");
>> --
>> 1.9.3
> 
> .
> 


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