Commit Graph

4 Commits

Author SHA1 Message Date
Jonas Devlieghere a4b42c621b [llvm] Protect signpost map with a mutex
Use a mutex to protect concurrent access to the signpost map. This fixes
nondeterministic crashes in LLDB that appeared after using signposts in
the timer implementation.

Differential revision: https://reviews.llvm.org/D94285
2021-01-19 11:41:54 -08:00
Jonas Devlieghere b37de2afa3 [Support] Untie the llvm::Signpost interface from llvm::Timer
Make llvm::Signpost more generic by untying from llvm::Timer. This
allows signposts to be used in a different context.

My motivation for doing this is being able to use signposts in LLDB.

Differential revision: https://reviews.llvm.org/D93655
2021-01-06 15:16:09 -08:00
Sven van Haastregt 0096d1938e [Support] Fix Wundef warning
llvm-svn: 368984
2019-08-15 10:05:22 +00:00
Daniel Sanders e1414d1760 Annotate timeline in Instruments with passes and other timed regions.
Summary:
Instruments is a useful tool for finding performance issues in LLVM but it can
be difficult to identify regions of interest on the timeline that we can use
to filter the profiler or allocations instrument. Xcode 10 and the latest
macOS/iOS/etc. added support for the os_signpost() API which allows us to
annotate the timeline with information that's meaningful to LLVM.

This patch causes timer start and end events to emit signposts. When used with
-time-passes, this causes the passes to be annotated on the Instruments timeline.
In addition to visually showing the duration of passes on the timeline, it also
allows us to filter the profile and allocations instrument down to an individual
pass allowing us to find the issues within that pass without being drowned out
by the noise from other parts of the compiler.

Using this in conjunction with the Time Profiler (in high frequency mode) and
the Allocations instrument is how I found the SparseBitVector that should have
been a BitVector and the DenseMap that could be replaced by a sorted vector a
couple months ago. I added NamedRegionTimers to TableGen and used the resulting
annotations to identify the slow portions of the Register Info Emitter. Some of
these were placed according to educated guesses while others were placed
according to hot functions from a previous profile. From there I filtered the
profile to a slow portion and the aforementioned issues stood out in the
profile.

To use this feature enable LLVM_SUPPORT_XCODE_SIGNPOSTS in CMake and run the
compiler under Instruments with -time-passes like so:
  instruments -t 'Time Profiler' bin/llc -time-passes -o - input.ll'
Then open the resulting trace in Instruments.

There was a talk at WWDC 2018 that explained the feature which can be found at
https://developer.apple.com/videos/play/wwdc2018/405/ if you'd like to know
more about it.

Reviewers: bogner

Reviewed By: bogner

Subscribers: jdoerfert, mgorny, kristina, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D52954

llvm-svn: 354365
2019-02-19 18:18:31 +00:00