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

[Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>]

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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