From: Yusuke Endoh <mame@...>
Date: 2014-01-08T00:31:00+09:00
Subject: [ruby-core:59632] Re: [ruby-trunk - Feature #9362][Assigned] Minimize cache misshit to gain optimal speed

Hello,

2014/1/7 Urabe Shyouhei <shyouhei@ruby-lang.org>:
> My experiment on valgrind clearly shows decreasing number of L1 data read
> misshits.  I can say that at least.

Something is wrong.  In principle, using more memory should make cache
miss increase.
In fact, when I replicate your experiment with "perf stat", the number
of L1-dcache-load-misses increases about 1.5x: 3,846,577 -> 5,665,965.

Note that the elapsed time does not change in spite of the increased
cache misses.
So, I think there is actually an improvement.  But I guess it is not
due to cache misses.  There should be another reason.


# trunk
$ perf stat -e L1-dcache-load-misses -e cache-misses ./ruby
--disable-gems -e "0x400000.times { Object.new }"

 Performance counter stats for './ruby --disable-gems -e
0x400000.times { Object.new }':

         3,922,093 L1-dcache-load-misses
            69,527 cache-misses

       0.473115927 seconds time elapsed

# shyouhei/cachelined
$ perf stat -e L1-dcache-load-misses -e cache-misses ./ruby
--disable-gems -e "0x400000.times { Object.new }"

 Performance counter stats for './ruby --disable-gems -e
0x400000.times { Object.new }':

         5,644,399 L1-dcache-load-misses
            82,589 cache-misses

       0.473268687 seconds time elapsed

-- 
Yusuke Endoh <mame@tsg.ne.jp>