Patch to increase the number of tlb entries a guest uses

Patch to increase the number of tlb entries a guest uses

[Christian Ehrhardt]

Hi Scott,
I just discussed with Hollis about shadow tlb management in the 
hypervisor and he mentioned that you already have a patch that lets the 
guest use more tlb entries than it would have on bare metal hardware and 
therefore allow to handle more tlb misses in the host because the shadow 
tlb already holds that information.

It would be nice if you could provide me and the kvmppc community that 
patch, because I wanted to modify our tlb handling a bit. If it would be 
easy enough I would like to test that with a different number of guest 
tlb entries too to see how big the impact of such a change would be to 
our shadow tlb management.


-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization

Re: Patch to increase the number of tlb entries a guest uses

[Scott Wood]

On Mon, Oct 20, 2008 at 06:46:29PM +0200, Christian Ehrhardt wrote:
> Hi Scott,
> I just discussed with Hollis about shadow tlb management in the 
> hypervisor and he mentioned that you already have a patch that lets the 
> guest use more tlb entries than it would have on bare metal hardware and 
> therefore allow to handle more tlb misses in the host because the shadow 
> tlb already holds that information.
> 
> It would be nice if you could provide me and the kvmppc community that 
> patch, because I wanted to modify our tlb handling a bit. If it would be 
> easy enough I would like to test that with a different number of guest 
> tlb entries too to see how big the impact of such a change would be to 
> our shadow tlb management.

It's not a patch to KVM, it's something I've done on Freescale's
hypervisor (which isn't released yet).

-Scott

Re: Patch to increase the number of tlb entries a guest uses

[Hollis Blanchard]

On Tue, 2008-10-21 at 08:27 -0500, Scott Wood wrote:
> On Mon, Oct 20, 2008 at 06:46:29PM +0200, Christian Ehrhardt wrote:
> > Hi Scott,
> > I just discussed with Hollis about shadow tlb management in the 
> > hypervisor and he mentioned that you already have a patch that lets the 
> > guest use more tlb entries than it would have on bare metal hardware and 
> > therefore allow to handle more tlb misses in the host because the shadow 
> > tlb already holds that information.
> > 
> > It would be nice if you could provide me and the kvmppc community that 
> > patch, because I wanted to modify our tlb handling a bit. If it would be 
> > easy enough I would like to test that with a different number of guest 
> > tlb entries too to see how big the impact of such a change would be to 
> > our shadow tlb management.
> 
> It's not a patch to KVM, it's something I've done on Freescale's
> hypervisor (which isn't released yet).

I think Christian was referring to the Linux side of it. But I guess
that since Freescale parts have TLBCFG registers advertising the size of
the TLBs, there wouldn't necessarily be any Linux changes at all. (Hmm,
that's pretty nice. :)

-- 
Hollis Blanchard
IBM Linux Technology Center

Re: Patch to increase the number of tlb entries a guest uses

[Scott Wood]

On Tue, Oct 21, 2008 at 08:55:46AM -0500, Hollis Blanchard wrote:
> On Tue, 2008-10-21 at 08:27 -0500, Scott Wood wrote:
> > It's not a patch to KVM, it's something I've done on Freescale's
> > hypervisor (which isn't released yet).
> 
> I think Christian was referring to the Linux side of it. But I guess
> that since Freescale parts have TLBCFG registers advertising the size of
> the TLBs, there wouldn't necessarily be any Linux changes at all. (Hmm,
> that's pretty nice. :)

Correct, there are no Linux changes for this.  Actually, we can't quite
advertise the size of the TLB we use in TLB0CFG, since there aren't
enough bits -- but Linux doesn't care.

-Scott