Re: [RFC v5 00/38] powerpc: Memory Protection Keys

From: Ram Pai
Date: Mon Jul 10 2017 - 13:16:01 EST

On Sun, Jul 09, 2017 at 11:05:44PM -0700, Ram Pai wrote:
> On Mon, Jul 10, 2017 at 11:13:23AM +0530, Anshuman Khandual wrote:
> > On 07/06/2017 02:51 AM, Ram Pai wrote:
> > do you have data points to show the difference in
> > performance between this version and the last one where
> > we skipped the bits from PTE and directly programmed the
> > HPTE entries looking into VMA bits.
> No. I dont. I am hoping you can help me out with this.
The last version where we skipped the PTE bits is guaranteed
to be bad/horrible. For one it has a bug, since it accesses
the vma without a lock. And even if we did take a lock, it
will slow down the page-hash path un-acceptably. So there is
no point measuring the performance of that design.

I think the number we want to measure is -- the performance
with the current design and comparing that to the performance
without memkey feature. We want to find if there is
any degradation by adding this feature.