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

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 30 Oct 2017 17:19:31 +0530

Paul Mackerras <[email-masked]> 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 looked at the perf data and with the test, we are doing larger number
of hash faults and then around 10k flush_hash_range. Can the small
improvement in number be due to the fact that we are not storing slot
number when doing an insert now?. Also in the flush path we are now not
using real_pte_t.

aneesh