[BOLT] Make memory profile parsing optional

[aaupov]

Introduce parse-mem-profile option to limit overheads processing
tracing data (Intel PT or ARM ETM). By default, it's enabled for
perf data (existing behavior), unless itrace is passed to parse
tracing data where it's extremely expensive.

[llvmbot]

@llvm/pr-subscribers-clang-driver
@llvm/pr-subscribers-clang
@llvm/pr-subscribers-lldb

@llvm/pr-subscribers-bolt

Author: Amir Ayupov (aaupov)

Changes

Introduce parse-mem-profile option (on by default) to control
whether perf2bolt will attempt to extract memory profile from perf data.

The use case is tracing data (ARM SPE or Intel PT) where synthesizing
memory profile is extremely expensive. Memory profile parsing will be
switched off by default when working with trace data (based on itrace
flag).

---

Full diff: https://github.com/llvm/llvm-project/pull/129585.diff

1 Files Affected:

• (modified) bolt/lib/Profile/DataAggregator.cpp (+29-20)

diff --git a/bolt/lib/Profile/DataAggregator.cpp b/bolt/lib/Profile/DataAggregator.cpp
index d20626bd5062f..909ec32477468 100644
--- a/bolt/lib/Profile/DataAggregator.cpp
+++ b/bolt/lib/Profile/DataAggregator.cpp
@@ -61,6 +61,12 @@ FilterMemProfile("filter-mem-profile",
   cl::init(true),
   cl::cat(AggregatorCategory));
 
+static cl::opt<bool> ParseMemProfile(
+    "parse-mem-profile",
+    cl::desc("enable memory profile parsing if it's present in the input data, "
+             "on by default unless `--itrace` is set."),
+    cl::init(true), cl::cat(AggregatorCategory));
+
 static cl::opt<unsigned long long>
 FilterPID("pid",
   cl::desc("only use samples from process with specified PID"),
@@ -177,6 +183,10 @@ void DataAggregator::start() {
                       "script -F pid,event,ip",
                       /*Wait = */false);
   } else if (!opts::ITraceAggregation.empty()) {
+    // Disable parsing memory profile from trace data, unless requested by user.
+    if (!opts::ParseMemProfile.getNumOccurrences())
+      opts::ParseMemProfile = false;
+
     std::string ItracePerfScriptArgs = llvm::formatv(
         "script -F pid,brstack --itrace={0}", opts::ITraceAggregation);
     launchPerfProcess("branch events with itrace", MainEventsPPI,
@@ -187,12 +197,9 @@ void DataAggregator::start() {
                       /*Wait = */ false);
   }
 
-  // Note: we launch script for mem events regardless of the option, as the
-  //       command fails fairly fast if mem events were not collected.
-  launchPerfProcess("mem events",
-                    MemEventsPPI,
-                    "script -F pid,event,addr,ip",
-                    /*Wait = */false);
+  if (opts::ParseMemProfile)
+    launchPerfProcess("mem events", MemEventsPPI, "script -F pid,event,addr,ip",
+                      /*Wait = */ false);
 
   launchPerfProcess("process events", MMapEventsPPI,
                     "script --show-mmap-events --no-itrace",
@@ -213,7 +220,8 @@ void DataAggregator::abort() {
   sys::Wait(TaskEventsPPI.PI, 1, &Error);
   sys::Wait(MMapEventsPPI.PI, 1, &Error);
   sys::Wait(MainEventsPPI.PI, 1, &Error);
-  sys::Wait(MemEventsPPI.PI, 1, &Error);
+  if (opts::ParseMemProfile)
+    sys::Wait(MemEventsPPI.PI, 1, &Error);
 
   deleteTempFiles();
 
@@ -464,13 +472,6 @@ Error DataAggregator::preprocessProfile(BinaryContext &BC) {
     exit(1);
   };
 
-  auto MemEventsErrorCallback = [&](int ReturnCode, StringRef ErrBuf) {
-    Regex NoData("Samples for '.*' event do not have ADDR attribute set. "
-                 "Cannot print 'addr' field.");
-    if (!NoData.match(ErrBuf))
-      ErrorCallback(ReturnCode, ErrBuf);
-  };
-
   if (BC.IsLinuxKernel) {
     // Current MMap parsing logic does not work with linux kernel.
     // MMap entries for linux kernel uses PERF_RECORD_MMAP
@@ -511,13 +512,21 @@ Error DataAggregator::preprocessProfile(BinaryContext &BC) {
       (opts::BasicAggregation && parseBasicEvents()))
     errs() << "PERF2BOLT: failed to parse samples\n";
 
-  // Special handling for memory events
-  if (prepareToParse("mem events", MemEventsPPI, MemEventsErrorCallback))
-    return Error::success();
+  if (opts::ParseMemProfile) {
+    auto MemEventsErrorCallback = [&](int ReturnCode, StringRef ErrBuf) {
+      Regex NoData("Samples for '.*' event do not have ADDR attribute set. "
+                   "Cannot print 'addr' field.");
+      if (!NoData.match(ErrBuf))
+        ErrorCallback(ReturnCode, ErrBuf);
+    };
 
-  if (const std::error_code EC = parseMemEvents())
-    errs() << "PERF2BOLT: failed to parse memory events: " << EC.message()
-           << '\n';
+    if (prepareToParse("mem events", MemEventsPPI, MemEventsErrorCallback))
+      return Error::success();
+
+    if (const std::error_code EC = parseMemEvents())
+      errs() << "PERF2BOLT: failed to parse memory events: " << EC.message()
+             << '\n';
+  }
 
   deleteTempFiles();