[PATCH v2 0/4] tracing: Have filters and histograms use a call table instead of pointers

[Steven Rostedt]

While looking at the histogram and filter code, I realized that it's filled
with function pointers. With retpolines causing a big slowdown, I thought
that was problematic. Thus, I decided to see what would happen if I changed
the function pointers into enums, and instead called a single function
that did a switch on those enums and called the necessary functions
directly. The results were pretty clear.

The first patch was to update the trace event benchmark event to include
a integer value "delta" of the delta that it took to complete
(it currently only shows the delta as part of a string). By doing
so, I could benchmark the histogram and filter logic with it.

Before this series, the histogram with a single filter (to ignore the
first event, which has a delta of zero), had:

# event histogram
#
# trigger info: hist:keys=delta:vals=hitcount:sort=delta:size=2048 if delta > 0 [active]
#

{ delta:        129 } hitcount:       2213
{ delta:        130 } hitcount:     285965
{ delta:        131 } hitcount:    1146545
{ delta:        132 } hitcount:    5185432
{ delta:        133 } hitcount:   19896215
{ delta:        134 } hitcount:   53118616
{ delta:        135 } hitcount:   83816709
{ delta:        136 } hitcount:   68329562
{ delta:        137 } hitcount:   41859349
{ delta:        138 } hitcount:   46257797
{ delta:        139 } hitcount:   54400831
{ delta:        140 } hitcount:   72875007
{ delta:        141 } hitcount:   76193272
{ delta:        142 } hitcount:   49504263
{ delta:        143 } hitcount:   38821072
{ delta:        144 } hitcount:   47702679
{ delta:        145 } hitcount:   41357297
{ delta:        146 } hitcount:   22058238
{ delta:        147 } hitcount:    9720002
{ delta:        148 } hitcount:    3193542
{ delta:        149 } hitcount:     927030
{ delta:        150 } hitcount:     850772
{ delta:        151 } hitcount:    1477380
{ delta:        152 } hitcount:    2687977
{ delta:        153 } hitcount:    2865985
{ delta:        154 } hitcount:    1977492
{ delta:        155 } hitcount:    2475607
{ delta:        156 } hitcount:    3403612
{ delta:        157 } hitcount:    2264011
{ delta:        158 } hitcount:    1096214
{ delta:        159 } hitcount:     504653
{ delta:        160 } hitcount:     218869
{ delta:        161 } hitcount:     103246
[..]

Where the bulk was around 142ns, and the fastest time was 129ns.

After this series:

# event histogram
#
# trigger info: hist:keys=delta:vals=hitcount:sort=delta:size=2048 if delta > 0 [active]
#

{ delta:        103 } hitcount:         60
{ delta:        104 } hitcount:      16966
{ delta:        105 } hitcount:     396625
{ delta:        106 } hitcount:    3223400
{ delta:        107 } hitcount:   12053754
{ delta:        108 } hitcount:   20241711
{ delta:        109 } hitcount:   14850200
{ delta:        110 } hitcount:    4946599
{ delta:        111 } hitcount:    3479315
{ delta:        112 } hitcount:   18698299
{ delta:        113 } hitcount:   62388733
{ delta:        114 } hitcount:   95803834
{ delta:        115 } hitcount:   58278130
{ delta:        116 } hitcount:   15364800
{ delta:        117 } hitcount:    5586866
{ delta:        118 } hitcount:    2346880
{ delta:        119 } hitcount:    1131091
{ delta:        120 } hitcount:     620896
{ delta:        121 } hitcount:     236652
{ delta:        122 } hitcount:     105957
{ delta:        123 } hitcount:     119107
{ delta:        124 } hitcount:      54494
{ delta:        125 } hitcount:      63856
{ delta:        126 } hitcount:      64454
{ delta:        127 } hitcount:      34818
{ delta:        128 } hitcount:      41446
{ delta:        129 } hitcount:      51242
{ delta:        130 } hitcount:      28361
{ delta:        131 } hitcount:      23926
{ delta:        132 } hitcount:      22253
{ delta:        133 } hitcount:      16994
{ delta:        134 } hitcount:      14970
{ delta:        135 } hitcount:      13464
{ delta:        136 } hitcount:      11452
{ delta:        137 } hitcount:      12212
{ delta:        138 } hitcount:      12280
{ delta:        139 } hitcount:       9127
{ delta:        140 } hitcount:       9553

Where the bulk was around 114ns and the fast time was 103ns.

That's almost a 20% speedup!!!

Changes since v1: https://lore.kernel.org/all/20220823214606.344269352@xxxxxxxxxxx/

 - Fixed combining constants (Masami Hiramatsu)

Steven Rostedt (Google) (4):
      tracing: Add numeric delta time to the trace event benchmark
      tracing/hist: Call hist functions directly via a switch statement
      tracing: Move struct filter_pred into trace_events_filter.c
      tracing/filter: Call filter predicate functions directly via a switch statement

----
 kernel/trace/trace.h               |  13 --
 kernel/trace/trace_benchmark.c     |   2 +-
 kernel/trace/trace_benchmark.h     |   8 +-
 kernel/trace/trace_events_filter.c | 239 ++++++++++++++++++++++++-----------
 kernel/trace/trace_events_hist.c   | 246 +++++++++++++++++++++++++------------
 5 files changed, 343 insertions(+), 165 deletions(-)