Subject: Re: [PATCH 00/16] Remove hash page table slot tracking from linux PTE

From: Paul Mackerras <[email-masked]>
Date: Fri, 27 Oct 2017 16:41:36 +1100

On Fri, Oct 27, 2017 at 10:57:13AM +0530, Aneesh Kumar K.V wrote:
> 
> 
> On 10/27/2017 10:04 AM, Paul Mackerras wrote:
> >How do we interpret these numbers?  Are they times, or speed?  Is
> >larger better or worse?
> 
> Sorry for not including the details. They are time in seconds. Test case is
> a modified mmap_bench included in powerpc/selftest.
> 
> >
> >Can you give us the mean and standard deviation for each set of 5
> >please?
> >
> 
> powernv without patch
> median= 51.432255
> stdev = 0.370835
> 
> with patch
> median = 50.739922
> stdev = 0.06419662
> 
> pseries without patch
> median = 116.617884
> stdev = 3.04531023
> 
> with patch no hcall
> median = 119.42494
> stdev = 0.85874552
> 
> with patch and hcall
> median = 117.735808
> stdev = 2.7624151

So on powernv, the patch set *improves* performance by about 1.3%
(almost 2 standard deviations).  Do we know why that is?

On pseries, performance is about 2.4% worse without new hcalls, but
that is less than 1 standard deviation.  With new hcalls, performance
is 0.95% worse, only a third of a standard deviation.  I think we need
to do more measurements to try to get a more accurate picture here.

Were the pseries numbers done on KVM or PowerVM?  Could you do a set
of measurements on the other one too please?  (I assume the numbers
with the new hcall were done on KVM, and can't be done on PowerVM.)

Paul.