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

[Aneesh Kumar K.V]

Paul Mackerras <paulus at ozlabs.org> writes:

> 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?

I haven't looked at that closely. I was considering it within runtime
variance (no impact with patch series). I will get perf record collected
and will see if that points to any details.

>
> 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.)
>


The above pseries numbers were collected on KVM.

PowerVM numbers on a different machine:
Without patch
31.194165                           
31.372913                           
31.253494
31.416198
31.199180
MEDIAN = 31.253494
STDEV = 0.1018900

With patch series
31.538281
31.385996
31.492737
31.452514
31.259461
MEDIAN = 31.452514
STDEV  = 0.108511

-aneesh