Re: [PATCH 0 of 6] PowerPC KVM patches for 2.6.29

[Hollis Blanchard <hollisb@us.ibm.com>]

On Wed, 2008-12-03 at 13:32 +0200, Avi Kivity wrote:
> Hollis Blanchard wrote:
> > Hi Avi, here's the latest batch of PowerPC kernel patches.
> >
> > The first set dramatically improve performance. Most importantly, we add
> > support for large host pages with KVM (i.e. PAGE_SHIFT > 12). (Large *guest*
> > pages have already been supported since day 1, since the guest kernel uses
> > them for the linear map.) Followup patches further improve performance by
> > changing how we manage the shadow TLB.
> >
> > The last two add some accounting code to easily discover performance
> > bottlenecks. This is especially important since the 440 core lacks performance
> > monitoring hardware.
> >
> > These patches, in conjunction with 64KB pages on guest and host, get us to 96%
> > of native performance for compute-bound workloads, which I'm pretty happy
> > with. See http://kvm.qumranet.com/kvmwiki/PowerPC_Exittimings for more
> > details (those statistics were gathered using the accounting patches).
> >
> > These have been tested pretty thoroughly for several weeks. Please apply for
> > 2.6.29. Thanks!
> >   
> 
> Applied all, thanks.

Thanks.

> I'm not thrilled about the private exit timing statistics gathering, 
> hopefully it can be morphed into the more general framework.

Is there anything in particular you have in mind? I think it could be
generally useful, but since x86 has hardware support for performance
monitoring, oprofile will already give you more accurate information. Of
course, I don't think you could extract standard deviation from an
oprofile report, and that has been very useful for us because it can
tell us e.g. 99% of instruction emulation is handled in the minimum
amount of time, but 1% takes hundreds of ms.

I'll let Christian comment when he gets back from vacation on Monday.

-- 
Hollis Blanchard
IBM Linux Technology Center