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subscriber: add more benchmarks for filters #581

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merged 5 commits into from
Feb 12, 2020
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@hawkw hawkw commented Feb 12, 2020

Motivation

Currently, there are a few cases that aren't adequately covered by the
tracing-subscriber filtering benchmarks. In particular, we don't have
benchmarks which involve filters with multiple directives, missing a
large amount of potential overhead from iterating over the directive
set, and we don't have benchmarks for events generated by the log
integration. Since log events can't participate in the callsite
caching mechanism, their performance picture is radically different.

Solution

This branch adds new benchmarks for filters with multiple static
directives, filters with multiple dynamic directives, and filters with
mixed static and dynamic directives. Additionally, I've added a new set
of benchmarks which are identical to the current ones, except that
log's macros are used to emit events via tracing-log, rather than
using tracing's macros directly.

Current Results

Benchmark environment
eliza@ares:~$ uname -a
Linux ares 4.9.0-11-amd64 #1 SMP Debian 4.9.189-3+deb9u2 (2019-11-11) x86_64 GNU/Linux
eliza@ares:~$ rustc --version
rustc 1.41.0 (5e1a79984 2020-01-27)
eliza@ares:~$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                40
On-line CPU(s) list:   0-39
Thread(s) per core:    2
Core(s) per socket:    10
Socket(s):             2
NUMA node(s):          2
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 79
Model name:            Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz
Stepping:              1
CPU MHz:               2200.000
CPU max MHz:           2200.0000
CPU min MHz:           1200.0000
BogoMIPS:              4390.06
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              25600K
NUMA node0 CPU(s):     0-9,20-29
NUMA node1 CPU(s):     10-19,30-39
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb invpcid_single kaiser tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdseed adx smap intel_pt xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm arat pln pts
Benchmark results
    Finished bench [optimized] target(s) in 50.95s
     Running target/release/deps/filter-b804f035b8022c0d
static/baseline_single_threaded
                        time:   [109.09 ns 109.37 ns 109.89 ns]
Found 14 outliers among 100 measurements (14.00%)
  4 (4.00%) high mild
  10 (10.00%) high severe
static/single_threaded  time:   [63.893 ns 63.951 ns 64.022 ns]
Found 14 outliers among 100 measurements (14.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
  11 (11.00%) high severe
static/enabled_one      time:   [28.293 ns 28.321 ns 28.355 ns]
Found 9 outliers among 100 measurements (9.00%)
  3 (3.00%) high mild
  6 (6.00%) high severe
static/enabled_many     time:   [28.278 ns 28.292 ns 28.311 ns]
Found 15 outliers among 100 measurements (15.00%)
  2 (2.00%) low mild
  5 (5.00%) high mild
  8 (8.00%) high severe
static/disabled_level_one
                        time:   [3.6514 ns 3.6545 ns 3.6580 ns]
Found 15 outliers among 100 measurements (15.00%)
  5 (5.00%) high mild
  10 (10.00%) high severe
static/disabled_level_many
                        time:   [4.1064 ns 4.1118 ns 4.1189 ns]
Found 13 outliers among 100 measurements (13.00%)
  2 (2.00%) low mild
  1 (1.00%) high mild
  10 (10.00%) high severe
static/disabled_one     time:   [4.1063 ns 4.1307 ns 4.1673 ns]
Found 12 outliers among 100 measurements (12.00%)
  1 (1.00%) low mild
  11 (11.00%) high severe
static/disabled_many    time:   [4.1091 ns 4.1136 ns 4.1190 ns]
Found 13 outliers among 100 measurements (13.00%)
  3 (3.00%) high mild
  10 (10.00%) high severe
static/baseline_multithreaded
                        time:   [7.2856 us 7.4135 us 7.5423 us]
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe
static/multithreaded    time:   [7.5089 us 7.6710 us 7.8466 us]
Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
  1 (1.00%) high severe

dynamic/baseline_single_threaded
                        time:   [247.58 ns 247.78 ns 247.98 ns]
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) high mild
  1 (1.00%) high severe
dynamic/single_threaded time:   [1.2122 us 1.2131 us 1.2141 us]
Found 7 outliers among 100 measurements (7.00%)
  3 (3.00%) high mild
  4 (4.00%) high severe
dynamic/baseline_multithreaded
                        time:   [7.3576 us 7.5858 us 7.8602 us]
Found 5 outliers among 100 measurements (5.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
  2 (2.00%) high severe
dynamic/multithreaded   time:   [8.2427 us 8.4257 us 8.6156 us]
Found 5 outliers among 100 measurements (5.00%)
  2 (2.00%) high mild
  3 (3.00%) high severe

mixed/disabled          time:   [80.464 ns 80.534 ns 80.611 ns]
Found 7 outliers among 100 measurements (7.00%)
  2 (2.00%) low mild
  3 (3.00%) high mild
  2 (2.00%) high severe
mixed/disabled_by_level time:   [68.077 ns 68.113 ns 68.155 ns]
Found 5 outliers among 100 measurements (5.00%)
  2 (2.00%) low severe
  2 (2.00%) high mild
  1 (1.00%) high severe

     Running target/release/deps/filter_log-b8cedd42cccfa727
log/static/baseline_single_threaded
                        time:   [477.71 ns 478.03 ns 478.40 ns]
Found 9 outliers among 100 measurements (9.00%)
  7 (7.00%) high mild
  2 (2.00%) high severe
log/static/single_threaded
                        time:   [553.40 ns 554.14 ns 555.17 ns]
Found 6 outliers among 100 measurements (6.00%)
  5 (5.00%) high mild
  1 (1.00%) high severe
log/static/enabled_one  time:   [172.29 ns 172.47 ns 172.68 ns]
Found 21 outliers among 100 measurements (21.00%)
  14 (14.00%) high mild
  7 (7.00%) high severe
log/static/enabled_many time:   [172.49 ns 172.61 ns 172.75 ns]
Found 10 outliers among 100 measurements (10.00%)
  4 (4.00%) high mild
  6 (6.00%) high severe
log/static/disabled_level_one
                        time:   [78.422 ns 78.529 ns 78.651 ns]
Found 17 outliers among 100 measurements (17.00%)
  2 (2.00%) high mild
  15 (15.00%) high severe
log/static/disabled_level_many
                        time:   [128.72 ns 128.83 ns 128.98 ns]
Found 8 outliers among 100 measurements (8.00%)
  2 (2.00%) low mild
  6 (6.00%) high severe
log/static/disabled_one time:   [77.385 ns 77.579 ns 77.848 ns]
Found 10 outliers among 100 measurements (10.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  8 (8.00%) high severe
log/static/disabled_many
                        time:   [123.67 ns 123.84 ns 124.03 ns]
Found 2 outliers among 100 measurements (2.00%)
  2 (2.00%) high mild
log/static/baseline_multithreaded
                        time:   [7.4644 us 7.6093 us 7.7570 us]
Found 2 outliers among 100 measurements (2.00%)
  2 (2.00%) high mild
log/static/multithreaded
                        time:   [7.5466 us 7.7412 us 7.9768 us]
Found 4 outliers among 100 measurements (4.00%)
  2 (2.00%) low mild
  2 (2.00%) high mild

log/dynamic/baseline_single_threaded
                        time:   [615.96 ns 616.53 ns 617.29 ns]
Found 8 outliers among 100 measurements (8.00%)
  3 (3.00%) high mild
  5 (5.00%) high severe
log/dynamic/single_threaded
                        time:   [1.4436 us 1.4457 us 1.4483 us]
Found 2 outliers among 100 measurements (2.00%)
  1 (1.00%) high mild
  1 (1.00%) high severe
log/dynamic/baseline_multithreaded
                        time:   [7.3015 us 7.5285 us 7.8139 us]
Found 6 outliers among 100 measurements (6.00%)
  1 (1.00%) low severe
  3 (3.00%) high mild
  2 (2.00%) high severe
log/dynamic/multithreaded
                        time:   [7.9638 us 8.2182 us 8.5184 us]
Found 7 outliers among 100 measurements (7.00%)
  2 (2.00%) low mild
  2 (2.00%) high mild
  3 (3.00%) high severe

log/mixed/disabled      time:   [104.93 ns 105.01 ns 105.12 ns]
Found 10 outliers among 100 measurements (10.00%)
  3 (3.00%) low mild
  7 (7.00%) high severe
log/mixed/disabled_by_level
                        time:   [91.754 ns 92.322 ns 93.531 ns]
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) low mild
  2 (2.00%) high severe

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw requested a review from a team February 12, 2020 22:56
@hawkw hawkw self-assigned this Feb 12, 2020
@hawkw hawkw added crate/subscriber Related to the `tracing-subscriber` crate kind/maintenance labels Feb 12, 2020
@hawkw
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hawkw commented Feb 12, 2020

I've cherry-picked this change from a separate branch so we can easily run these benchmarks against master & establish a baseline, before merging some performance improvements.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
@hawkw hawkw merged commit 409baff into master Feb 12, 2020
hawkw added a commit that referenced this pull request Feb 14, 2020
…ce (#583)

## Motivation

The benchmarks added in #581 indicate that `tracing-subscriber`'s 
`EnvFilter` has significant overhead when filtering events generated
from `log` records that is not present when filtering native `tracing` 
events.

Additionally, the behavior of `EnvFilter` differs from the `env_logger`
crate it emulates: when a less specific filter is more verbose than a
more specific filter, the more verbose filter is used. For example:

```
RUST_LOG=debug,tokio_postgres=info,hyper::server::response=info
```

* With `env_logger` - treat all targets as DEBUG *except* for 
  `tokio_postgres` and `hyper::server::response`

* With `EnvFilter::from_default_env()` - treat all targets as DEBUG.
  This then overrides the explicit setting of INFO for the other two,
  so they are DEBUG as well.

(see #512)

## Solution

This branch makes some performance optimizations to filtering, to
improve performance with `log` events significantly. In particular, it
makes the following changes:

* Code was previously added to record the maximum level enabled by
  the static and dynamic directive sets. This would allow a fast path
  for skipping events that no directive will ever enable. However, this
  currently is never actually checked, so we always have to check an
  event against every directive. I've fixed that.

* If there are no dynamic directives that would require looking at the
  dynamic span state (a TLS value), we now avoid looking at TLS.

* Finally, I've fixed #512, by changing `enabled` to select the _most_
  specific static filter, rather than by checking _every_ filter until
  it finds something that enables the span. In addition to making the
  behaviour correct, this also improves performance: it means we only 
  iterate over the statics until we find something that cares about an
  event, and then return. In the previous implementation (of incorrect 
  behavior), we would break the iteration if the event was enabled, but
  never break iteration if it was disabled. Now, we can return early.
  This should improve performance significantly with a large number of 
  filters.

## Benchmark Results

Performance in the `filter_log` benchmark is significantly improved in
most cases, while performance in the `filter` benchmark (for filtering
`tracing` events) is about the same as master, but significantly better
than `filter_log` across the board. This is expected, since the
`tracing` events in `filter` benchmark can (in most cases) participate
in the callsite cache, while the `log` events cannot. Therefore, the
`filter` benchmarks with static filters are measuring the overhead of a
single filter hit + multiple callsite cache loads, while the
`filter_log` benchmarks are always measuring an actual filter hit.


<details>
<summary>Benchmark results (vs master):</summary>

```console
eliza@ares:~/tracing$ cargo bench -p tracing-subscriber --bench filter --bench filter_log
   Compiling tracing-subscriber v0.2.0 (/home/eliza/tracing/tracing-subscriber)
    Finished bench [optimized] target(s) in 9.86s
     Running target/release/deps/filter-b804f035b8022c0d
static/baseline_single_threaded
                        time:   [109.11 ns 109.21 ns 109.32 ns]
                        change: [-6.3289% -4.9555% -3.6799%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 11 outliers among 100 measurements (11.00%)
  2 (2.00%) high mild
  9 (9.00%) high severe
static/single_threaded  time:   [62.942 ns 63.023 ns 63.150 ns]
                        change: [-0.1370% +0.0191% +0.2011%] (p = 0.83 > 0.05)
                        No change in performance detected.
Found 15 outliers among 100 measurements (15.00%)
  1 (1.00%) low mild
  6 (6.00%) high mild
  8 (8.00%) high severe
static/enabled_one      time:   [28.745 ns 28.764 ns 28.789 ns]
                        change: [-0.2144% -0.0862% +0.0283%] (p = 0.18 > 0.05)
                        No change in performance detected.
Found 13 outliers among 100 measurements (13.00%)
  1 (1.00%) low mild
  4 (4.00%) high mild
  8 (8.00%) high severe
static/enabled_many     time:   [28.765 ns 28.827 ns 28.912 ns]
                        change: [-0.0864% +0.2092% +0.5574%] (p = 0.25 > 0.05)
                        No change in performance detected.
Found 16 outliers among 100 measurements (16.00%)
  5 (5.00%) high mild
  11 (11.00%) high severe
static/disabled_level_one
                        time:   [4.1104 ns 4.1134 ns 4.1170 ns]
                        change: [+0.0402% +0.1317% +0.2300%] (p = 0.01 < 0.05)
                        Change within noise threshold.
Found 13 outliers among 100 measurements (13.00%)
  5 (5.00%) high mild
  8 (8.00%) high severe
static/disabled_level_many
                        time:   [3.6496 ns 3.6530 ns 3.6573 ns]
                        change: [-0.2017% -0.0164% +0.1271%] (p = 0.86 > 0.05)
                        No change in performance detected.
Found 15 outliers among 100 measurements (15.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  13 (13.00%) high severe
static/disabled_one     time:   [3.6496 ns 3.6517 ns 3.6543 ns]
                        change: [-0.1254% +0.1413% +0.5468%] (p = 0.52 > 0.05)
                        No change in performance detected.
Found 14 outliers among 100 measurements (14.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  12 (12.00%) high severe
static/disabled_many    time:   [3.6501 ns 3.6518 ns 3.6538 ns]
                        change: [-0.0351% +0.0331% +0.1054%] (p = 0.35 > 0.05)
                        No change in performance detected.
Found 15 outliers among 100 measurements (15.00%)
  2 (2.00%) low mild
  2 (2.00%) high mild
  11 (11.00%) high severe
static/baseline_multithreaded
                        time:   [7.6316 us 7.8421 us 8.0892 us]
                        change: [-1.1385% +2.9646% +7.3036%] (p = 0.18 > 0.05)
                        No change in performance detected.
Found 7 outliers among 100 measurements (7.00%)
  5 (5.00%) high mild
  2 (2.00%) high severe
static/multithreaded    time:   [7.5579 us 7.7286 us 7.9126 us]
                        change: [+0.2480% +3.6935% +7.1400%] (p = 0.04 < 0.05)
                        Change within noise threshold.
Found 4 outliers among 100 measurements (4.00%)
  3 (3.00%) high mild
  1 (1.00%) high severe

dynamic/baseline_single_threaded
                        time:   [245.73 ns 246.12 ns 246.67 ns]
                        change: [-2.6694% -2.3670% -2.0569%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 20 outliers among 100 measurements (20.00%)
  7 (7.00%) low mild
  2 (2.00%) high mild
  11 (11.00%) high severe
dynamic/single_threaded time:   [1.1532 us 1.1550 us 1.1568 us]
                        change: [+0.2317% +0.4117% +0.5707%] (p = 0.00 < 0.05)
                        Change within noise threshold.
Found 3 outliers among 100 measurements (3.00%)
  2 (2.00%) high mild
  1 (1.00%) high severe
dynamic/baseline_multithreaded
                        time:   [7.6121 us 7.7931 us 7.9882 us]
                        change: [-4.3847% +0.2323% +4.8431%] (p = 0.92 > 0.05)
                        No change in performance detected.
Found 3 outliers among 100 measurements (3.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  1 (1.00%) high severe
dynamic/multithreaded   time:   [8.0848 us 8.2926 us 8.5161 us]
                        change: [-2.0820% +1.4262% +4.9321%] (p = 0.42 > 0.05)
                        No change in performance detected.
Found 5 outliers among 100 measurements (5.00%)
  1 (1.00%) low mild
  4 (4.00%) high mild

mixed/disabled          time:   [67.544 ns 67.623 ns 67.716 ns]
                        change: [+4.0220% +4.3608% +4.6472%] (p = 0.00 < 0.05)
                        Performance has regressed.
Found 12 outliers among 100 measurements (12.00%)
  1 (1.00%) low mild
  1 (1.00%) high mild
  10 (10.00%) high severe
mixed/disabled_by_level time:   [26.704 ns 26.743 ns 26.785 ns]
                        change: [-51.833% -51.737% -51.632%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
  1 (1.00%) high severe

     Running target/release/deps/filter_log-b8cedd42cccfa727
log/static/baseline_single_threaded
                        time:   [459.87 ns 460.05 ns 460.28 ns]
                        change: [-4.4236% -4.3735% -4.3170%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 13 outliers among 100 measurements (13.00%)
  1 (1.00%) low severe
  4 (4.00%) low mild
  1 (1.00%) high mild
  7 (7.00%) high severe
log/static/single_threaded
                        time:   [469.18 ns 470.12 ns 471.08 ns]
                        change: [-12.406% -12.037% -11.759%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high severe
log/static/enabled_one  time:   [154.79 ns 155.08 ns 155.54 ns]
                        change: [-10.717% -10.585% -10.436%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 11 outliers among 100 measurements (11.00%)
  1 (1.00%) low mild
  4 (4.00%) high mild
  6 (6.00%) high severe
log/static/enabled_many time:   [229.55 ns 229.69 ns 229.86 ns]
                        change: [-11.433% -11.076% -10.828%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 4 outliers among 100 measurements (4.00%)
  3 (3.00%) high mild
  1 (1.00%) high severe
log/static/disabled_level_one
                        time:   [57.489 ns 57.518 ns 57.557 ns]
                        change: [-20.363% -20.247% -20.155%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  2 (2.00%) high mild
  5 (5.00%) high severe
log/static/disabled_level_many
                        time:   [57.486 ns 57.515 ns 57.554 ns]
                        change: [-48.696% -48.652% -48.610%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  1 (1.00%) high mild
  5 (5.00%) high severe
log/static/disabled_one time:   [68.872 ns 68.902 ns 68.941 ns]
                        change: [-4.0195% -3.8865% -3.7487%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 10 outliers among 100 measurements (10.00%)
  2 (2.00%) low mild
  8 (8.00%) high severe
log/static/disabled_many
                        time:   [103.10 ns 103.38 ns 103.72 ns]
                        change: [-5.8728% -5.6128% -5.3436%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 6 outliers among 100 measurements (6.00%)
  3 (3.00%) high mild
  3 (3.00%) high severe
log/static/baseline_multithreaded
                        time:   [7.5054 us 7.7234 us 7.9713 us]
                        change: [-4.8650% -1.5881% +2.0839%] (p = 0.37 > 0.05)
                        No change in performance detected.
Found 4 outliers among 100 measurements (4.00%)
  3 (3.00%) high mild
  1 (1.00%) high severe
log/static/multithreaded
                        time:   [7.6285 us 7.7574 us 7.8967 us]
                        change: [-4.5998% -2.0115% +0.5929%] (p = 0.14 > 0.05)
                        No change in performance detected.
Found 1 outliers among 100 measurements (1.00%)
  1 (1.00%) high mild

log/dynamic/baseline_single_threaded
                        time:   [603.16 ns 603.55 ns 603.96 ns]
                        change: [-6.9548% -6.7858% -6.6651%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 20 outliers among 100 measurements (20.00%)
  3 (3.00%) high mild
  17 (17.00%) high severe
log/dynamic/single_threaded
                        time:   [1.4624 us 1.4645 us 1.4669 us]
                        change: [+4.2866% +4.4193% +4.5763%] (p = 0.00 < 0.05)
                        Performance has regressed.
Found 4 outliers among 100 measurements (4.00%)
  1 (1.00%) high mild
  3 (3.00%) high severe
log/dynamic/baseline_multithreaded
                        time:   [7.6292 us 7.8527 us 8.1103 us]
                        change: [-6.4268% -2.6258% +0.8495%] (p = 0.17 > 0.05)
                        No change in performance detected.
Found 9 outliers among 100 measurements (9.00%)
  1 (1.00%) low mild
  8 (8.00%) high mild
log/dynamic/multithreaded
                        time:   [8.0253 us 8.2673 us 8.5647 us]
                        change: [-3.4243% +0.5838% +5.0749%] (p = 0.79 > 0.05)
                        No change in performance detected.
Found 6 outliers among 100 measurements (6.00%)
  2 (2.00%) low mild
  1 (1.00%) high mild
  3 (3.00%) high severe

log/mixed/disabled      time:   [94.775 ns 94.825 ns 94.884 ns]
                        change: [-0.0623% +0.0665% +0.1997%] (p = 0.33 > 0.05)
                        No change in performance detected.
Found 11 outliers among 100 measurements (11.00%)
  2 (2.00%) low mild
  1 (1.00%) high mild
  8 (8.00%) high severe
log/mixed/disabled_by_level
                        time:   [59.763 ns 59.809 ns 59.873 ns]
                        change: [-26.225% -26.054% -25.852%] (p = 0.00 < 0.05)
                        Performance has improved.
Found 12 outliers among 100 measurements (12.00%)
  1 (1.00%) low mild
  2 (2.00%) high mild
  9 (9.00%) high severe

```

</details>

<details>

<summary>Benchmark environment:</summary>

```console
eliza@ares:~/tracing$ uname -a
Linux ares 4.9.0-11-amd64 #1 SMP Debian 4.9.189-3+deb9u2 (2019-11-11) x86_64 GNU/Linux
eliza@ares:~/tracing$ rustc --version
rustc 1.41.0 (5e1a79984 2020-01-27)
eliza@ares:~/tracing$ lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                40
On-line CPU(s) list:   0-39
Thread(s) per core:    2
Core(s) per socket:    10
Socket(s):             2
NUMA node(s):          2
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 79
Model name:            Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz
Stepping:              1
CPU MHz:               1879.077
CPU max MHz:           2200.0000
CPU min MHz:           1200.0000
BogoMIPS:              4390.06
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              25600K
NUMA node0 CPU(s):     0-9,20-29
NUMA node1 CPU(s):     10-19,30-39
Flags:                 fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch epb invpcid_single kaiser tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm cqm rdseed adx smap intel_pt xsaveopt cqm_llc cqm_occup_llc cqm_mbm_total cqm_mbm_local dtherm arat pln pts
eliza@ares:~/tracing$
```

</details>

Fixes #512

Signed-off-by: Eliza Weisman <eliza@buoyant.io>
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