linux/tools
Kan Liang 121f325f34 perf evsel: Only fall back group read for leader
Perf doesn't support mixed events from different PMUs (except software
event) in a group. The perf stat should output <not counted>/<not
supported> for all events, but it doesn't. For example,

  perf stat -e '{cycles,uncore_imc_5/umask=0xF,event=0x4/,instructions}'
       <not counted>      cycles
       <not supported>    uncore_imc_5/umask=0xF,event=0x4/
           1,024,300      instructions

If perf fails to open an event, it doesn't error out directly. It will
disable some features and retry, until the event is opened or all
features are disabled. The disabled features will not be re-enabled. The
group read is one of these features.

For the example as above, the IMC event and the leader event "cycles"
are from different PMUs. Opening the IMC event must fail. The group read
feature must be disabled for IMC event and the followed event
"instructions". The "instructions" event has the same PMU as the leader
"cycles". It can be opened successfully. Since the group read feature
has been disabled, the "instructions" event will be read as a single
event, which definitely has a value.

The group read fallback is still useful for the case which kernel
doesn't support group read. It is good enough to be handled only by the
leader.

For the fallback request from members, it must be caused by an error.
The fallback only breaks the semantics of group.  Limit the group read
fallback only for the leader.

Committer testing:

On a broadwell t450s notebook:

Before:

  # perf stat -e '{cycles,unc_cbo_cache_lookup.read_i,instructions}' sleep 1

  Performance counter stats for 'sleep 1':

     <not counted>      cycles
   <not supported>      unc_cbo_cache_lookup.read_i
           818,206      instructions

       1.003170887 seconds time elapsed

  Some events weren't counted. Try disabling the NMI watchdog:
	echo 0 > /proc/sys/kernel/nmi_watchdog
	perf stat ...
	echo 1 > /proc/sys/kernel/nmi_watchdog

After:

  # perf stat -e '{cycles,unc_cbo_cache_lookup.read_i,instructions}' sleep 1

  Performance counter stats for 'sleep 1':

     <not counted>      cycles
   <not supported>      unc_cbo_cache_lookup.read_i
     <not counted>      instructions

       1.001380511 seconds time elapsed

  Some events weren't counted. Try disabling the NMI watchdog:
	echo 0 > /proc/sys/kernel/nmi_watchdog
	perf stat ...
	echo 1 > /proc/sys/kernel/nmi_watchdog
  #

Reported-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Agustin Vega-Frias <agustinv@codeaurora.org>
Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will.deacon@arm.com>
Fixes:  82bf311e15 ("perf stat: Use group read for event groups")
Link: http://lkml.kernel.org/r/1524594014-79243-3-git-send-email-kan.liang@linux.intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2018-04-24 16:11:59 -03:00
..
accounting
arch tools/headers: Synchronize kernel ABI headers, v4.17-rc1 2018-04-17 09:47:39 -03:00
bpf Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net 2018-04-01 19:49:34 -04:00
build Kbuild: fix # escaping in .cmd files for future Make 2018-04-11 00:03:02 +09:00
cgroup tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
firewire
gpio Linux 4.16-rc5 2018-03-18 17:48:59 +01:00
hv tools: hv: include string.h in hv_fcopy_daemon 2018-03-06 09:57:16 -08:00
iio tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
include coresight: Move to SPDX identifier 2018-04-19 12:29:41 -03:00
kvm/kvm_stat tools/kvm_stat: Remove unused function 2018-03-28 22:47:06 +02:00
laptop tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
leds tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
lib perf tools: Add '\n' at the end of parse-options error messages 2018-04-18 15:35:51 -03:00
memory-model tools/memory-model: Finish the removal of rb-dep, smp_read_barrier_depends(), and lockless_dereference() 2018-03-10 10:22:23 +01:00
nfsd
objtool Kbuild: fix # escaping in .cmd files for future Make 2018-04-11 00:03:02 +09:00
pci
pcmcia
perf perf evsel: Only fall back group read for leader 2018-04-24 16:11:59 -03:00
power Power management updates for 4.17-rc1 2018-04-03 10:45:39 -07:00
scripts Kbuild: fix # escaping in .cmd files for future Make 2018-04-11 00:03:02 +09:00
spi tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
testing proc: fixup copyright sign 2018-04-12 20:52:25 -07:00
thermal/tmon tools/thermal: tmon: fix for segfault 2018-03-27 09:51:23 +02:00
time
usb usbip: tools: usbipd: exclude exported devices from exportable device list 2018-03-22 13:08:20 +01:00
virtio ptr_ring: fix build 2018-03-20 03:17:37 +02:00
vm tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
wmi tools: fix cross-compile var clobbering 2018-02-21 15:35:42 -08:00
Makefile