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Namhyung Kim 57482dc5ac perf sort: Fix the 'weight' sort key behavior 
[ Upstream commit 784e8adda4 ]

Currently, the 'weight' field in the perf sample has latency information
for some instructions like in memory accesses.  And perf tool has 'weight'
and 'local_weight' sort keys to display the info.

But it's somewhat confusing what it shows exactly.  In my understanding,
'local_weight' shows a weight in a single sample, and (global) 'weight'
shows a sum of the weights in the hist_entry.

For example:

  $ perf mem record -t load dd if=/dev/zero of=/dev/null bs=4k count=1M

  $ perf report --stdio -n -s +local_weight
  ...
  #
  # Overhead  Samples  Command  Shared Object     Symbol                     Local Weight
  # ........  .......  .......  ................  .........................  ............
  #
      21.23%      313  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   32
      12.43%      183  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   35
      11.97%      159  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   36
      10.40%      141  dd       [kernel.vmlinux]  [k] lockref_put_return     32
       7.63%      113  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   33
       6.37%       92  dd       [kernel.vmlinux]  [k] lockref_get_not_zero   34
       6.15%       90  dd       [kernel.vmlinux]  [k] lockref_put_return     33
  ...

So let's look at the 'lockref_get_not_zero' symbols.  The top entry
shows that 313 samples were captured with 'local_weight' 32, so the
total weight should be 313 x 32 = 10016.  But it's not the case:

  $ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
  ...
  #
  # Overhead  Samples  Command  Shared Object     Local Weight  Weight
  # ........  .......  .......  ................  ............  ......
  #
       1.36%        4  dd       [kernel.vmlinux]  36            144
       0.47%        4  dd       [kernel.vmlinux]  37            148
       0.42%        4  dd       [kernel.vmlinux]  32            128
       0.40%        4  dd       [kernel.vmlinux]  34            136
       0.35%        4  dd       [kernel.vmlinux]  36            144
       0.34%        4  dd       [kernel.vmlinux]  35            140
       0.30%        4  dd       [kernel.vmlinux]  36            144
       0.30%        4  dd       [kernel.vmlinux]  34            136
       0.30%        4  dd       [kernel.vmlinux]  32            128
       0.30%        4  dd       [kernel.vmlinux]  32            128
  ...

With the 'weight' sort key, it's divided to 4 samples even with the same
info ('comm', 'dso', 'sym' and 'local_weight').  I don't think this is
what we want.

I found this because of the way it aggregates the 'weight' value.  Since
it's not a period, we should not add them in the he->stat.  Otherwise,
two 32 'weight' entries will create a 64 'weight' entry.

After that, new 32 'weight' samples don't have a matching entry so it'd
create a new entry and make it a 64 'weight' entry again and again.
Later, they will be merged into 128 'weight' entries during the
hists__collapse_resort() with 4 samples, multiple times like above.

Let's keep the weight and display it differently.  For 'local_weight',
it can show the weight as is, and for (global) 'weight' it can display
the number multiplied by the number of samples.

With this change, I can see the expected numbers.

  $ perf report --stdio -n -s +local_weight,weight -S lockref_get_not_zero
  ...
  #
  # Overhead  Samples  Command  Shared Object     Local Weight  Weight
  # ........  .......  .......  ................  ............  .....
  #
      21.23%      313  dd       [kernel.vmlinux]  32            10016
      12.43%      183  dd       [kernel.vmlinux]  35            6405
      11.97%      159  dd       [kernel.vmlinux]  36            5724
       7.63%      113  dd       [kernel.vmlinux]  33            3729
       6.37%       92  dd       [kernel.vmlinux]  34            3128
       4.17%       59  dd       [kernel.vmlinux]  37            2183
       0.08%        1  dd       [kernel.vmlinux]  269           269
       0.08%        1  dd       [kernel.vmlinux]  38            38

Reviewed-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20211105225617.151364-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2021-12-08 09:04:40 +01:00
arch s390/setup: avoid using memblock_enforce_memory_limit 2021-12-08 09:04:39 +01:00
block block: avoid to quiesce queue in elevator_init_mq 2021-12-01 09:04:56 +01:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: pcrypt - Delay write to padata->info 2021-11-18 19:16:44 +01:00
Documentation docs: accounting: update delay-accounting.rst reference 2021-12-01 09:04:56 +01:00
drivers net: ethernet: dec: tulip: de4x5: fix possible array overflows in type3_infoblock() 2021-12-08 09:04:40 +01:00
fs btrfs: check-integrity: fix a warning on write caching disabled disk 2021-12-08 09:04:39 +01:00
include net: ipv6: add fib6_nh_release_dsts stub 2021-12-01 09:04:49 +01:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc shm: extend forced shm destroy to support objects from several IPC nses 2021-11-25 09:48:42 +01:00
kernel tracing: Check pid filtering when creating events 2021-12-01 09:04:55 +01:00
lib printk: restore flushing of NMI buffers on remote CPUs after NMI backtraces 2021-11-25 09:48:45 +01:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm hugetlbfs: flush TLBs correctly after huge_pmd_unshare 2021-11-25 09:49:07 +01:00
net ipv6: check return value of ipv6_skip_exthdr 2021-12-08 09:04:40 +01:00
samples samples/bpf: Fix incorrect use of strlen in xdp_redirect_cpu 2021-11-25 09:48:33 +01:00
scripts leaking_addresses: Always print a trailing newline 2021-11-18 19:16:16 +01:00
security selinux: fix NULL-pointer dereference when hashtab allocation fails 2021-11-25 09:49:07 +01:00
sound ALSA: usb-audio: Don't start stream for capture at prepare 2021-12-08 09:04:37 +01:00
tools perf sort: Fix the 'weight' sort key behavior 2021-12-08 09:04:40 +01:00
usr .gitignore: prefix local generated files with a slash 2021-05-02 00:43:35 +09:00
virt KVM: Remove tlbs_dirty 2021-09-23 11:01:12 -04:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS drm fixes for 5.15 final 2021-10-28 12:17:01 -07:00
Makefile Linux 5.15.6 2021-12-01 09:04:57 +01:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.