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

Daniel P. Berrange
2008-04-30T13:56:11Z

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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