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From: Stephane Eranian <eranian <at> google.com>
Subject: [PATCH v4 00/18] perf: add memory access sampling support
Newsgroups: gmane.linux.kernel
Date: Thursday 20th December 2012 15:41:30 UTC (over 3 years ago)
This patch series had a new feature to the kernel perf_events
interface and corresponding user level tool, perf.

With this patch, it is possible to sample (not trace) memory
accesses (load, store). For loads, the instruction and data
addresses are captured along with the latency and data source.
For stores, the instruction and data addresses are capture
along with limited cache and TLB information.

For load data source, the memory hierarchy level, the tlb, snoop
and lock information is captured.

Although the perf_event interface is extended in a generic manner,
sampling memory accesses requires HW support. The current patches
implement the feature on Intel processors starting with Nehalem.
The patches leverage the PEBS Load Latency and Precise Store
mechanisms. Precise Store is present only on Sandy Bridge and
Ivy Bridge based processors.

The perf tool is extended to make capturing and analyzing the
data easier with a new command: perf mem.

$ perf mem -t load rec triad
$ perf mem -t load rep --stdio
# Samples: 19K of event 'cpu/mem-loads/pp'
# Total cost : 1013994
# Sort order : cost,mem,sym,dso,symbol_daddr,dso_daddr,snoop,tlb,locked
# Overhead      Samples     Cost  Memory access Symbol      Shared Obj 
Data Symbol             Data Object Snoop  TLB access   Locked
# ........  ...........  .......  ............. ..........  ...........
......................  ........... ...... ............ ......
     0.10%            1      986  LFB hit       [.] triad   triad       [.]
0x00007f67dffe8038  [unknown]    None  L1 or L2 hit  No    
     0.09%            1      890  LFB hit       [.] triad   triad       [.]
0x00007f67df91a750  [unknown]    None  L1 or L2 hit  No    
     0.08%            1      826  LFB hit       [.] triad   triad       [.]
0x00007f67e288fba8  [unknown]    None  L1 or L2 hit  No    
     0.08%            1      825  LFB hit       [.] triad   triad       [.]
0x00007f67dea28c80  [unknown]    None  L1 or L2 hit  No    
     0.08%            1      787  LFB hit       [.] triad   triad       [.]
0x00007f67df055a60  [unknown]    None  L1 or L2 hit  No    

The perf mem command is a wrapper around perf record/report. It passes the
right options to the report and record commands. Note that the TUI mode is

One powerful feature of perf is that users can toy with sort order to
the information in different format or from a different angle. This is
useful with memory sampling:

$ perf mem -t load rep --sort=mem
# Samples: 19K of event 'cpu/mem-loads/pp'
# Total cost : 1013994
# Sort order : mem
# Overhead      Samples             Memory access
# ........  ...........  ........................
    85.26%        10633  LFB hit                 
     7.35%         8151  L1 hit                  
     3.13%          383  L3 hit                  
     3.09%          195  Local RAM hit           
     1.16%          259  L2 hit                  
     0.00%            4  Uncached hit            

Or if one is interested in the data view:
$ perf mem -t load rep --sort=symbol_daddr,cost
# Samples: 19K of event 'cpu/mem-loads/pp'
# Total cost : 1013994
# Sort order : symbol_daddr,cost
# Overhead      Samples             Data Symbol     Cost
# ........  ...........  ......................  .......
     0.10%            1  [.] 0x00007f67dffe8038      986
     0.09%            1  [.] 0x00007f67df91a750      890
     0.08%            1  [.] 0x00007f67e288fba8      826

One note on the cost displayed: On Intel processors with PEBS Load Latency,
as described
in the SDM, the cost encompasses the number of cycles from dispatch to
Globally Observable
(GO) state. That means, that it includes OOO execution. It is not usual to
see L1D Hits
with a cost of > 100 cycles. Always look at the memory level for an
approximation of the
access penalty, then interpret the cost value accordingly.

Data symbolization is working for initialized global variables. Dynamically
data and bss symbolization is currently non-functional.

There is no cost associated with stores.

In v2, we leverage some of Andi Kleen's Haswell patches, namely the
samples and perf tool event parser fixes. We  also introduce
to tag mmaps for data vs. code. This helps the perf tool distinguish data.
vs. code
mmaps (and therefore symbols). We have also integrated the feedback from
v1. Note that in
v2 data symbol resolution is not yet fully operational, but there is a
slight improvement.

In v3, we rebased the patch on 3.7.0-rc6 which includes certain of
Nahyung's patches.

In v4, we rebase to v3.7 tip and also included the fixes from Namhyung Kim
symbolization of data addresses. We now have accesses to global variables

Andi Kleen (2):
  perf, x86: Support CPU specific sysfs events
  perf, core: Add a concept of a weightened sample

Namhyung Kim (2):
  perf tools: Ignore ABS symbols when loading data maps
  perf tools: Fix output of symbol_daddr offset

Stephane Eranian (14):
  perf/x86: improve sysfs event mapping with event string
  perf/x86: add flags to event constraints
  perf: add minimal support for PERF_SAMPLE_WEIGHT
  perf: add support for PERF_SAMPLE_ADDR in dump_sampple()
  perf: add generic memory sampling interface
  perf/x86: add memory profiling via PEBS Load Latency
  perf/x86: export PEBS load latency threshold register to sysfs
  perf/x86: add support for PEBS Precise Store
  perf tools: add mem access sampling core support
  perf report: add support for mem access profiling
  perf record: add support for mem access profiling
  perf tools: add new mem command for memory access profiling
  perf tools: detect data vs. text mappings

 arch/x86/include/uapi/asm/msr-index.h         |    1 +
 arch/x86/kernel/cpu/perf_event.c              |   63 +++--
 arch/x86/kernel/cpu/perf_event.h              |   62 ++++-
 arch/x86/kernel/cpu/perf_event_intel.c        |   34 ++-
 arch/x86/kernel/cpu/perf_event_intel_ds.c     |  182 +++++++++++++-
 arch/x86/kernel/cpu/perf_event_intel_uncore.c |    2 +-
 include/linux/perf_event.h                    |    5 +
 include/uapi/linux/perf_event.h               |   74 +++++-
 kernel/events/core.c                          |   15 ++
 tools/perf/Makefile                           |    1 +
 tools/perf/builtin-mem.c                      |  238 ++++++++++++++++++
 tools/perf/builtin-record.c                   |    2 +
 tools/perf/builtin-report.c                   |  131 +++++++++-
 tools/perf/builtin.h                          |    1 +
 tools/perf/command-list.txt                   |    1 +
 tools/perf/perf.c                             |    1 +
 tools/perf/perf.h                             |    1 +
 tools/perf/util/event.h                       |    2 +
 tools/perf/util/evsel.c                       |   15 ++
 tools/perf/util/hist.c                        |   67 ++++-
 tools/perf/util/hist.h                        |   13 +
 tools/perf/util/machine.c                     |   10 +-
 tools/perf/util/session.c                     |   44 ++++
 tools/perf/util/session.h                     |    4 +
 tools/perf/util/sort.c                        |  324
 tools/perf/util/sort.h                        |   10 +-
 tools/perf/util/symbol-elf.c                  |    3 +
 tools/perf/util/symbol.h                      |    7 +
 28 files changed, 1264 insertions(+), 49 deletions(-)
 create mode 100644 tools/perf/builtin-mem.c

CD: 19ms