Re: [RFC PATCH 0/3] generic hypercall support

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Gregory Haskins wrote:
> Avi Kivity wrote:
>> David S. Ahern wrote:
>>> I ran another test case with SMT disabled, and while I was at it
>>> converted TSC delta to operations/sec. The results without SMT are
>>> confusing -- to me anyways. I'm hoping someone can explain it.
>>> Basically, using a count of 10,000,000 (per your web page) with SMT
>>> disabled the guest detected a soft lockup on the CPU. So, I dropped the
>>> count down to 1,000,000. So, for 1e6 iterations:
>>>
>>> without SMT, with EPT:
>>>     HC:   259,455 ops/sec
>>>     PIO:  226,937 ops/sec
>>>     MMIO: 113,180 ops/sec
>>>
>>> without SMT, without EPT:
>>>     HC:   274,825 ops/sec
>>>     PIO:  247,910 ops/sec
>>>     MMIO: 111,535 ops/sec
>>>
>>> Converting the prior TSC deltas:
>>>
>>> with SMT, with EPT:
>>>     HC:    994,655 ops/sec
>>>     PIO:   875,116 ops/sec
>>>     MMIO:  439,738 ops/sec
>>>
>>> with SMT, without EPT:
>>>     HC:    994,304 ops/sec
>>>     PIO:   903,057 ops/sec
>>>     MMIO:  423,244 ops/sec
>>>
>>> Running the tests repeatedly I did notice a fair variability (as much as
>>> -10% down from these numbers).
>>>
>>> Also, just to make sure I converted the delta to ops/sec, the formula I
>>> used was cpu_freq / dTSC * count = operations/sec
>>>
>>>   
>> The only think I can think of is cpu frequency scaling lying about the
>> cpu frequency.  Really the test needs to use time and not the time
>> stamp counter.
>>
>> Are the results expressed in cycles/op more reasonable?
> 
> FWIW: I always used kvm_stat instead of my tsc printk
> 

kvm_stat shows same approximate numbers as with the TSC-->ops/sec
conversions. Interestingly, MMIO writes are not showing up as mmio_exits
in kvm_stat; they are showing up as insn_emulation.

david
> 
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