Re: performance with guests running 2.4 kernels (specifically RHEL3)

Avi Kivity
2008-04-30T13:49:55Z

David S. Ahern wrote:
> Avi Kivity wrote:
>
>> David S. Ahern wrote:
>>
>>> Another tidbit for you guys as I make my way through various
>>> permutations:
>>> I installed the RHEL3 hugemem kernel and the guest behavior is *much*
>>> better.
>>> System time still has some regular hiccups that are higher than xen
>>> and esx
>>> (e.g., 1 minute samples out of 5 show system time between 10 and 15%),
>>> but
>>> overall guest behavior is good with the hugemem kernel.
>>>
>>>
>>>
>> Wait, the amount of info here is overwhelming. Let's stick with the
>> current kernel (32-bit, HIGHMEM4G, right?)
>>
>> Did you get any traces with bypass_guest_pf=0? That may show more info.
>>
>>
>
> My preference is to stick with the "standard", 32-bit RHEL3 kernel in the guest.
>

Me too. I would like to see all reasonable guests supported well,
without performance issues, and not have to tell the use which kernel to
use.

> My point in the last email was that the hugemem kernel shows a remarkable
> difference (it uses 3-levels of page tables right?). I was hoping that would
> ring a bell with someone.
>

From the traces I saw I think the standard kernel is pae as well. Can
you verify? I think it's CONFIG_HIGHMEM4G (instead of
CONFIG_HIGHMEM64G) but that option may be different for such an old kernel.

> Adding bypass_guest_pf=0 did not improve the situation. Did you want anything
> particular with that setting -- like a RIP summary or a summary of exit-entry
> cycles?
>

I asked fo this thinking bypass_guest_pf may help show more
information. But thinking a bit more, it will not.

I think I do know what the problem is. I will try it out. Is there a
free clone (like centos) available somewhere?

--
Any sufficiently difficult bug is indistinguishable from a feature.

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