| commit | 9fd9e418858c3414eabbeb5031fa193579575555 | [log] [tgz] |
|---|---|---|
| author | Lalit Maganti <lalitm@google.com> | Thu Sep 26 11:27:21 2019 +0100 |
| committer | Lalit Maganti <lalitm@google.com> | Thu Sep 26 11:27:21 2019 +0100 |
| tree | 9a59bcf299ec127924b1f92ea96f42c147379da5 | |
| parent | 53fa633591c3418823b82d844f22e3ad9abd7e97 [diff] |
trace_processor: break Append -> Append{True,False} and Set -> Set,Clear
This CL changes the Append and Set methods of bitvector to stop taking a
bool parameter but instead have explicit methods for the true and false
variant.
There are a few reasons for doing this:
1. In most real world usage of bitvector, we will actually be passing
a constant so having separate methods allows the compiler to better
inline and optimize
2. Even if the vector<bool> implementation looks like it would write
the bit to the storage, it's actually far more efficient to have
both methods according to the benchmarks (see below)
3. In the upcoming refactor of bitvector, having the separate methods
is an order of magnitude more efficient and changing this in the old
code allows for more accurate benchmark comparisions.
Old numbers:
-----------------------------------------------------------------
Benchmark Time CPU Iterations
-----------------------------------------------------------------
BM_BitVectorAppend 6 ns 6 ns 118772108
BM_BitVectorSet 5 ns 5 ns 145386020
BM_BitVectorIndexOfNthSet 173538 ns 173538 ns 4010
BM_BitVectorGetNumBitsSet 2930 ns 2930 ns 240818
New numbers:
-----------------------------------------------------------------
Benchmark Time CPU Iterations
-----------------------------------------------------------------
BM_BitVectorAppendTrue 2 ns 2 ns 352256359
BM_BitVectorAppendFalse 2 ns 2 ns 352757342
BM_BitVectorSet 1 ns 1 ns 553163208
BM_BitVectorClear 1 ns 1 ns 536258728
BM_BitVectorIndexOfNthSet 171802 ns 171775 ns 4010
BM_BitVectorGetNumBitsSet 2904 ns 2903 ns 229680
Analysis:
As we can see, having separate append methods cuts timings from
6ns -> 2 ns and separate Set/Clear cuts from 5ns -> 1ns!
Context: go/perfetto-tp-refactor
Bug: 135177627
Change-Id: Iec3bf9b8633391b10e29b97124db90b602f2d9f6Perfetto is an open-source project for performance instrumentation and tracing of Linux/Android/Chrome platforms and user-space apps.
See www.perfetto.dev for docs.