RE: [Xen-ia64-devel] [IPF-ia64] with Cset 10690, creating a VTImake xen0 hang

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

Hi Alex,
        When VTI-domain does IO operation, an event is sent to dom0, then
Qemu is woken up to handle this request. Process switch on dom0 may call itr_d,
if task_struct of qemu is not covered by TR. But the emulation of itr_d is very 
slow, due to purge vhpt. This is the root cause of slowness of vti-domain boot
on your side, and vti-domain can't boot on my side.

        I think purging vhpt in emulating itr_d also slow down dom0 and domU,
So the question is, is purging vhpt in emulating itr_d necessary?

Thanks,
Anthony

>-----Original Message-----
>From: xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx
>[mailto:xen-ia64-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Zhang,
>Xiantao
>Sent: 2006年7月12日 10:56
>To: Atsushi SAKAI; Alex Williamson
>Cc: Isaku Yamahata; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>Subject: RE: [Xen-ia64-devel] [IPF-ia64] with Cset 10690,creating a VTImake
>xen0 hang
>
>Hi Alex,
>       Our QA team reported that xen0 would hang after creating VTi domain 
> @CSet
>10688-10694. Should we reverse the logic of vcpu_itr_d first ?  Maybe we can
>find out the real bottleneck later.:)
>Thanks & Best Regards
>-Xiantao
>
>OTC,Intel Corporation
>
>> -----Original Message-----
>> From: Atsushi SAKAI [mailto:sakaia@xxxxxxxxxxxxxx]
>> Sent: 2006年7月11日 21:46
>> To: Alex Williamson; Zhang, Xiantao
>> Cc: Isaku Yamahata; xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>> Subject: Re: [Xen-ia64-devel] [IPF-ia64] with Cset 10690, creating a VTImake
>> xen0 hang
>>
>> Hi, Alex
>>
>> Sorry for late.
>>
>> I found your problem(boot time difference w/ PAL_HALT_LIGHT emulation patch)
>> occurred in SMP(credit).
>> But, it does not occurred in UP, SMP(bvt) and SMP(credit w/ affinity).
>>
>> I think the emulation of pal_halt_light for domU
>> does not good work for DomVTI boot up
>> under credit scheduling w/o affinity.
>>
>> And consider the Xiantao survey,
>> qemu make heavy I/O operations at the boot up.
>>
>> Consider the above two conditions,
>> I think credit scheduler algorithm does not consider
>> the block state.(caused by pal_halt_light emulation)
>> So I want to switch off the vcpu migration at heavy load
>>
>>
>> I planned as follows.
>>
>> 1)In the short term,
>> I want to avoid this problem by
>> HALT the PAL_HALT_LIGHT emulation while DomVTI boot up.
>> or
>> Lock VCPUs migrations while DomVTI boot up.
>> (when Credit scheduler runs)
>>
>> 2)In the long term,
>> I will make a patch to avoid this problem.
>> (Consider the heavy io w/ vcpu migration)
>>
>> N.B.
>> I checked under CS:10559.(original patch made)
>>
>> Thanks,
>> Atsushi SAKAI
>>
>>
>>
>>
>>
>> >On Tue, 2006-07-11 at 19:42 +0800, Zhang, Xiantao wrote:
>> >> Hi Alex,
>> >>   Seems this issue was caused by Cset 10688. In vcpu_itr_d, the current
>> >> logic purges vhpt with cpu_flush_vhpt_range but it is very heavy to
>> >> xen0. When creating VTi domain @ early stage, IO operation is very
>> >> excessive, so qemu was scheduled out and in very frequently and this
>> >> logic was executed every time. In addition, cpu_flush_vhpt_range using
>> >> identity map to purge vhpt may cause more tlb miss due to no TR map.
>> >> If remove vcpu_flush_tlb_vhpt_range logic although it definitely
>> >> needed, seems VTi becomes healthy. Maybe potential bugs exist there.:)
>> >
>> >   Thanks for investigating Xiantao.  Isaku, any thoughts on how to
>> >regain VTI performance?  Thanks,
>> >
>> >    Alex
>> >
>> >--
>> >Alex Williamson                             HP Open Source & Linux Org.
>> >
>> >
>> >_______________________________________________
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>> >Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
>> >http://lists.xensource.com/xen-ia64-devel
>> >
>>
>>
>>
>
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