commit 2789b5bd404d06a4b97fc4d14c798528d4b3886b
author Daniele Di Proietto <ddiproietto@google.com> Fri Apr 14 09:53:03 2023 +0000
committer Daniele Di Proietto <ddiproietto@google.com> Fri May 05 14:42:33 2023 +0000
tree f7c05714a2edf270a54e09be7e42ed85140abbca
parent 3f822f4d245fb890e5957c9d70ecdda3be6d37dd

tracing_service_impl: Move compression from perfetto_cmd.cc

Before this change, trace compression was implemented in
perfetto_cmd.cc. This meant that it wasn't possible to use compression
with `write_into_file`, because the service would be directly writing
the data to a file, without going through perfetto_cmd.

With this commit the code that does the compression is moved into the
tracing service. Note that compression in the tracing service is only
enabled as part of `traced`, it's not enabled in the tracing service in
the client library (the compressor is injected with a function pointer).

Note that this change might have unexpected behavior when using
mismatching versions of perfetto_cmd and tracing_service (both will try
to compress or none will). In practice I'm not aware of any use of
mismatching versions, so I think it this will not be a problem.

The `compress_from_cli` config option can be used to restore the old
behavior (both in perfetto_cmd and tracing_service).

Here's the change in binary size for various files on android before and
after this patch:

```
| Binary                           | Size before | Size after |
| -------------------------------- | ----------- | ---------- |
| /system/bin/surfaceflinger       |     7445056 |    7445072 |
| /system/lib64/libgpumemtracer.so |      801936 |     806088 |
| /system/lib64/libperfetto.so     |     1124896 |    1125184 |
| /system/bin/perfetto             |      545176 |     545152 |
```

surfaceflinger and libgpumemtracer statically link the perfetto client
SDK. libperfetto.so contains the tracing service.

The last point to consider is that this makes the compression ratio a
little bit worse when write_into_file is not used. Before this patch,
perfetto_cmd was compressing as part of the same stream up to 512 Kb of
data. Now, reads from IPC are limited to 32 Kb, so that's how often we
have to reset the compression stream. In tested compressing 26 Mb of a
sample trace in both configurations and this are the results I got:

```
| Single stream size               | Total size | # of compressed packets |
| -------------------------------- | ---------- | ----------------------- |
| 32 Kb (after this patch)         |    9049943 |                     574 |
| 64 Kb                            |    8708512 |                     337 |
| 512 Kb (before this patch)       |    8306867 |                      50 |
```

Bug: 278884624

Change-Id: Ib777ba5c44930a53b3e95994e768a970822e70a3