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

David S. Ahern
2008-04-30T14:23:23Z

Yes, the 4G/4G patch and the 64G options are both enabled for the hugemem kernel:

CONFIG_HIGHMEM64G=y
CONFIG_X86_4G=y

Differences between the "standard" kernel and the hugemem kernel:

# diff config-2.4.21-47.ELsmp config-2.4.21-47.ELhugemem
2157,2158c2157,2158
< CONFIG_M686=y
< # CONFIG_MPENTIUMIII is not set
---
> # CONFIG_M686 is not set
> CONFIG_MPENTIUMIII=y
2169c2169
< CONFIG_X86_PGE=y
---
> # CONFIG_X86_PGE is not set
2193c2193
< # CONFIG_X86_4G is not set
---
> CONFIG_X86_4G=y
2365,2366c2365
< CONFIG_M686=y
< CONFIG_X86_PGE=y
---
> CONFIG_MPENTIUMIII=y
2369,2372d2367
< # CONFIG_MXT is not set
< CONFIG_HOTPLUG_PCI=y
< CONFIG_HOTPLUG_PCI_COMPAQ=m
< CONFIG_HOTPLUG_PCI_IBM=m
2373a2369
> CONFIG_X86_4G=y
2377,2379d2372
< # CONFIG_EWRK3 is not set
< CONFIG_UNIX98_PTY_COUNT=2048
< CONFIG_HZ=512
2382a2376,2383
> # CONFIG_MXT is not set
> CONFIG_HOTPLUG_PCI=y
> CONFIG_HOTPLUG_PCI_COMPAQ=m
> CONFIG_HOTPLUG_PCI_IBM=m
> # CONFIG_EWRK3 is not set
> CONFIG_UNIX98_PTY_COUNT=2048
> CONFIG_DEBUG_BUGVERBOSE=y
> # CONFIG_PNPBIOS is not set

Avi:

Centos releases:

http://isoredirect.centos.org/centos/3/isos/i386/

I am running RHEL3.8 which I do not see listed. Also, I'll need to work on a
stock install and try to capture some kind of workload that exhibits the
problem. It will be a couple of days.

david

Daniel P. Berrange wrote:
> On Wed, Apr 30, 2008 at 07:39:53AM -0600, 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.
>> 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.
>
> IIRC, the RHEL-3 hugemem kernel is using the 4g/4g split patches which
> give userspace and kernelspace their own independant pagetables
>
> http://lwn.net/Articles/39925/
> http://lwn.net/Articles/39283/
>
> Dan.

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