Jens Johansen
c56e94630e
This CL makes it possible for the Dart VM to start or stop `perf` while
doing GC, which gives a significantly more stable output.
Example usage:
Bash script that creates the correct file handles and calls dart under
`perf stat` based on the arguments given to the script:
```
DART=$1
shift
AOTSNAPSHOT=$1
shift
ctl_dir=/tmp/
ctl_fifo=${ctl_dir}perf_ctl.fifo
test -p ${ctl_fifo} && unlink ${ctl_fifo}
mkfifo ${ctl_fifo}
exec {ctl_fd}<>${ctl_fifo}
ctl_ack_fifo=${ctl_dir}perf_ctl_ack.fifo
test -p ${ctl_ack_fifo} && unlink ${ctl_ack_fifo}
mkfifo ${ctl_ack_fifo}
exec {ctl_fd_ack}<>${ctl_ack_fifo}
perf_ctl_fd=$ctl_fd perf_ctl_fd_ack=$ctl_fd_ack perf stat --delay=-1 --control fd:${ctl_fd},${ctl_fd_ack} -B -e "task-clock:u,context-switches:u,cpu-migrations:u,page-faults:u,cycles:u,instructions:u,branch-misses:u" $DART --perf_ctl_fd=${ctl_fd} --perf_ctl_fd_ack=${ctl_fd_ack} --perf_ctl_usage=1 --deterministic $AOTSNAPSHOT $@
exec {ctl_fd_ack}>&-
unlink ${ctl_ack_fifo}
exec {ctl_fd}>&-
unlink ${ctl_fifo}
```
This will start `perf stat` paused (which would require the run dart
aot-compiled script to start it when it wants to) and where the VM
pauses `perf` while doing GC.
In practise, looking at instruction counts reported by `perf stat`, I've
seen the difference between runs go from 2+ mio (and in some instances
23+ mio) to around 30,000 (!) on runs of the analyzer (tool
"stable_analysis").
TEST=manually
Change-Id: Iab955a5dd35e47f22c4f693ae50effc8ee633897
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/468260
Reviewed-by: Slava Egorov <vegorov@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>
1.4 KiB
Dart support for perf
Pause perf stat recording while GC is running (or vice versa)
perf stat supports starting and stopping the recording via --control and the
Dart VM can be instructed to either stop the recording while GC is running, or
specifically start while GC is running (and stop when GC is finished) with
--perf_ctl_fd, --perf_ctl_fd_ack (for file handles) and --perf_ctl_usage
(1 or 2) to specify if it should be paused while GCing (1) or started (and
stoped) while GCing (2).
These options can for instance be useful for testing performance changes in AOT
compiled dart together with --deterministic.
As an example one could run a script like this:
DART=$1
shift
AOTSNAPSHOT=$1
shift
[...]
perf_ctl_fd=$ctl_fd perf_ctl_fd_ack=$ctl_fd_ack perf stat --delay=-1 --control fd:${ctl_fd},${ctl_fd_ack} -B -e "task-clock:u,context-switches:u,cpu-migrations:u,page-faults:u,cycles:u,instructions:u,branch-misses:u" $DART --perf_ctl_fd=${ctl_fd} --perf_ctl_fd_ack=${ctl_fd_ack} --perf_ctl_usage=1 --deterministic $AOTSNAPSHOT $@
[...]
(the missing pieces can be found in the perf stat man page).
This will start perf stat paused (which would require the run dart
aot-compiled script to start it when it wants to) and where the VM pauses perf
while doing GC. Note that the recording will be started when GC is done, even if
it wasn't started before.