linux-kernel - perf stat stddev reporting broken since "perf stat: Introduce read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20160118175946.GC10802@techsingularity.net>
Date:	Mon, 18 Jan 2016 17:59:46 +0000
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Jiri Olsa <jolsa@...nel.org>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: perf stat stddev reporting broken since "perf stat: Introduce
 read_counters function"

I noticed that perf stat in 4.4 is not printing stddev figures as
expected and bisected it to commit 106a94a0f8c2 ("perf stat: Introduce
read_counters function").

# Kernel 4.4
# make clean && make prefix=/usr && ./perf stat -r 5 sleep 1
 Performance counter stats for 'sleep 1' (5 runs):

          0.466683      task-clock (msec)         #    0.000 CPUs utilized
                 1      context-switches          #    0.002 M/sec
                 1      cpu-migrations            #    0.002 M/sec
                66      page-faults               #    0.144 M/sec
         1,630,220      cycles                    #    3.562 GHz
   <not supported>      stalled-cycles-frontend
   <not supported>      stalled-cycles-backend
           902,686      instructions              #    0.66  insns per cycle
           185,692      branches                  #  405.786 M/sec
             8,640      branch-misses             #    4.63% of all branches

       1.000855883 seconds time elapsed           ( +-  0.01% )

# git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7^
 Performance counter stats for 'sleep 1' (5 runs):

          0.397939      task-clock (msec)         #    0.000 CPUs utilized            ( +-  3.37% )
                 1      context-switches          #    0.003 M/sec
                 0      cpu-migrations            #    0.000 K/sec
                67      page-faults               #    0.169 M/sec                    ( +-  0.56% )
         1,360,763      cycles                    #    3.420 GHz                      ( +-  2.14% )
   <not supported>      stalled-cycles-frontend
   <not supported>      stalled-cycles-backend
           903,901      instructions              #    0.66  insns per cycle          ( +-  0.24% )
           186,472      branches                  #  468.595 M/sec                    ( +-  0.29% )
             8,599      branch-misses             #    4.61% of all branches          ( +-  0.77% )

       1.000761882 seconds time elapsed                                               ( +-  0.00% )

# git checkout 106a94a0f8c207ef4113ce7e32f34a00b3b174e7

 Performance counter stats for 'sleep 1' (5 runs):

          0.583178      task-clock (msec)         #    0.001 CPUs utilized
                 1      context-switches          #    0.002 M/sec
                 0      cpu-migrations            #    0.000 K/sec
                67      page-faults               #    0.141 M/sec
         1,224,416      cycles                    #    2.585 GHz
   <not supported>      stalled-cycles-frontend
   <not supported>      stalled-cycles-backend
           892,568      instructions              #    0.68  insns per cycle
           184,975      branches                  #  390.554 M/sec
             8,512      branch-misses             #    4.57% of all branches

       1.000889249 seconds time elapsed                                          ( +-  0.01% )

I checked and current master in Linus' tree is also broken. Is this
change in documented perf stat behaviour intentional?

-- 
Mel Gorman
SUSE Labs