Do not set app nor extra library paths by default

By default, both paths pointed to the current working directory.
When I use perfparser in a folder that has many (sub)directories and
files, it is excruciatingly slow:

     145338.874552      task-clock (msec)         #    0.997 CPUs utilized
            13,353      context-switches          #    0.092 K/sec
               147      cpu-migrations            #    0.001 K/sec
             4,497      page-faults               #    0.031 K/sec
   557,953,349,806      cycles                    #    3.839 GHz
 1,009,672,374,742      instructions              #    1.81  insn per cycle
   238,669,106,565      branches                  # 1642.156 M/sec
     3,017,437,636      branch-misses             #    1.26% of all branches

     145.823501862 seconds time elapsed

This is on a SSD with an ext4 file system, but going through 104164
files for every mmap event is simply going to take its time.

This patch improves this situation by dropping the implicit recursive
lookup in the current working directory.

The performance impact is tremendous:

       4425.928440      task-clock (msec)         #    0.999 CPUs utilized
               158      context-switches          #    0.036 K/sec
                 1      cpu-migrations            #    0.000 K/sec
             3,299      page-faults               #    0.745 K/sec
    17,042,783,950      cycles                    #    3.851 GHz
    36,178,866,218      instructions              #    2.12  insn per cycle
     8,448,978,802      branches                  # 1908.973 M/sec
        63,738,579      branch-misses             #    0.75% of all branches

       4.432039578 seconds time elapsed

I.e. this patch makes this case more than 33 times faster.

Change-Id: I9a2c4e84ed739e1fc602be675bd01369b1c39f4c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

2 files changed, 10 insertions, 7 deletions

diff --git a/app/main.cpp b/app/main.cpp
index fee9055..eebb684 100644
--- a/app/main.cpp
+++ b/app/main.cpp
@@ -121,15 +121,13 @@ int main(int argc, char *argv[])
     QCommandLineOption extra(QLatin1String("extra"),
                              QCoreApplication::translate(
                                  "main", "Look for additional libraries in <path> (default: .)."),
-                             QLatin1String("path"),
-                             QLatin1String("."));
+                             QLatin1String("path"));
     parser.addOption(extra);
 
     QCommandLineOption appPath(QLatin1String("app"),
                                QCoreApplication::translate(
                                    "main", "Look for application binary in <path> (default: .)."),
-                               QLatin1String("path"),
-                               QLatin1String("."));
+                               QLatin1String("path"));
     parser.addOption(appPath);
 
     const auto defaultArch
diff --git a/app/perfsymboltable.cpp b/app/perfsymboltable.cpp
index a29cb30..c268426 100644
--- a/app/perfsymboltable.cpp
+++ b/app/perfsymboltable.cpp
@@ -170,6 +170,11 @@ static bool findInExtraPath(QFileInfo &path, const QString &fileName)
     return false;
 }
 
+static QStringList splitPath(const QString &path)
+{
+    return path.split(QLatin1Char(':'), QString::SkipEmptyParts);
+}
+
 void PerfSymbolTable::registerElf(const PerfRecordMmap &mmap, const QByteArray &buildId,
                                   const QString &appPath, const QString &systemRoot,
                                   const QString &extraLibsPath, const QString &debugInfoPath)
@@ -188,7 +193,7 @@ void PerfSymbolTable::registerElf(const PerfRecordMmap &mmap, const QByteArray &
         if (!buildId.isEmpty()) {
             const QString buildIdPath = QString::fromUtf8(mmap.filename() + '/'
                                                             + buildId.toHex() + "/elf");
-            foreach (const QString &extraPath, debugInfoPath.split(QLatin1Char(':'))) {
+            foreach (const QString &extraPath, splitPath(debugInfoPath)) {
                 fullPath.setFile(extraPath);
                 if (findInExtraPath(fullPath, buildIdPath)) {
                     found = true;
@@ -196,14 +201,14 @@ void PerfSymbolTable::registerElf(const PerfRecordMmap &mmap, const QByteArray &
                 }
             }
         }
-        if (!found) {
+        if (!found && !appPath.isEmpty()) {
             // try to find the file in the app path
             fullPath.setFile(appPath);
             found = findInExtraPath(fullPath, fileInfo.fileName());
         }
         if (!found) {
             // try to find the file in the extra libs path
-            foreach (const QString &extraPath, extraLibsPath.split(QLatin1Char(':'))) {
+            foreach (const QString &extraPath, splitPath(extraLibsPath)) {
                 fullPath.setFile(extraPath);
                 if (findInExtraPath(fullPath, fileInfo.fileName())) {
                     found = true;