Expand section on profilers (perf and VTune)

talk/tools/profiling.tex

@@ -4,39 +4,228 @@
   \frametitle{Profiling}
   \begin{block}{Conceptually}
     \begin{itemize}
-      \item take a measurement of a performance aspect of a program
+      \item Take a measurement of a performance aspect of a program
       \begin{itemize}
-        \item where in my code is most of the time spent?
-        \item is my program compute or memory bound?
-        \item does my program make good use of the cache?
-        \item is my program using all cores most of the time?
-        \item how often are threads blocked and why?
-        \item which API calls are made and in which order?
+        \item Where in my code is most of the time spent?
+        \item Is my program compute or memory bound?
+        \item Does my program make good use of the cache?
+        \item Is my program using all cores most of the time?
+        \item How often are threads blocked and why?
+        \item Which API calls are made and in which order?
         \item ...
       \end{itemize}
-      \item the goal is to find performance bottlenecks
-      \item is usually done on a compiled program, not on source code
+      \item The goal is to find performance bottlenecks
+      \item Usually done on a compiled program, not on source code
     \end{itemize}
   \end{block}
 \end{frame}
 
 \begin{frame}[fragile]
-  \frametitle{perf, VTune and uProf}
-  \begin{block}{perf}
+  \frametitle{\mintinline{bash}{perf} -- Performance analysis tools for Linux}
+  \setlength{\leftmargini}{0pt}
     \begin{itemize}
-      \item perf is a powerful command line profiling tool for linux
-      \item compile with \mintinline{bash}{-g -fno-omit-frame-pointer}
-      \item \mintinline{bash}{perf stat -d <prg>} gathers performance statistics while running \mintinline{bash}{<prg>}
-      \item \mintinline{bash}{perf record -g <prg>} starts profiling \mintinline{bash}{<prg>}
-      \item \mintinline{bash}{perf report} displays a report from the last profile
-      \item More information in \href{https://perf.wiki.kernel.org/index.php/Main_Page}{this wiki}, \href{https://www.brendangregg.com/linuxperf.html}{this website} or \href{https://indico.cern.ch/event/980497/contributions/4130271/attachments/2161581/3647235/linux-systems-performance.pdf}{this talk}.
+      \item Powerful command line profiling tool for Linux
+      \item Not portable, the source code is part of the Linux kernel itself
+      \item Much lower overhead compared with \mintinline{bash}{valgrind}
+      \item In order to profile your code, make sure to compile with
+            \texttt{CXXFLAGS="-O2 -g -fno-omit-frame-pointer"}
+      \item Counting and sampling
+        \begin{itemize}
+          \item Counting -- count occurrences of a given event (e.g.\ cache misses)
+          \item Time-based sampling -- sample the stack at regular time intervals
+          \item Event-based sampling -- take samples when event counter overflows
+          \item Instruction-based sampling -- sample instructions and precisely count events they create
+        \end{itemize}
+      \item Static and dynamic tracing
+        \begin{itemize}
+          \item Static -- pre-defined tracepoints in software (e.g.\ scheduling events)
+          \item Dynamic -- tracepoints created dynamically with \mintinline{bash}{perf probe}
+        \end{itemize}
     \end{itemize}
-  \end{block}
-  \begin{block}{Intel VTune and AMD uProf}
-    \begin{itemize}
-      \item Graphical profilers from CPU vendors with rich features
-      \item Needs vendor's CPU for full experience
-      \item More information on \href{https://www.intel.com/content/www/us/en/developer/tools/oneapi/vtune-profiler.html}{Intel's website} and \href{https://developer.amd.com/amd-uprof/}{AMD's website}
-    \end{itemize}
-  \end{block}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{\mintinline{bash}{perf} commands}
+  { \scriptsize
+    \begin{block}{}
+      \begin{minted}{shell-session}
+$ perf
+ usage: perf [--version] [--help] [OPTIONS] COMMAND [ARGS]
+ The most commonly used perf commands are:
+   annotate        Read perf.data and display annotated code
+   c2c             Shared Data C2C/HITM Analyzer.
+   config          Get and set variables in a configuration file.
+   diff            Read perf.data and display the differential profile
+   evlist          List the event names in a perf.data file
+   list            List all symbolic event types
+   mem             Profile memory accesses
+   record          Run a command and record its profile into perf.data
+   report          Read perf.data and display the profile
+   sched           Tool to trace/measure scheduler properties (latencies)
+   script          Read perf.data and display trace output
+   stat            Run command and gather performance counter statistics
+   top             System profiling tool.
+   version         display the version of perf binary
+   probe           Define new dynamic tracepoints
+   trace           strace inspired tool
+ See 'perf help COMMAND' for more information on a specific command.
+      \end{minted}
+    \end{block}
+  }
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Listing events with \mintinline{bash}{perf list}}
+  { \scriptsize
+    \begin{block}{}
+      \begin{minted}{shell-session}
+$ # List main hardware events
+$ perf list hw
+
+List of pre-defined events (to be used in -e):
+
+  branch-instructions OR branches                    [Hardware event]
+  branch-misses                                      [Hardware event]
+  cache-misses                                       [Hardware event]
+  cache-references                                   [Hardware event]
+  cpu-cycles OR cycles                               [Hardware event]
+  instructions                                       [Hardware event]
+
+$ # List main software/cache events
+$ perf list sw
+$ perf list cache
+
+$ # List all pre-defined metrics
+$ perf list metric
+
+$ # List all currently known events:
+$ perf list
+      \end{minted}
+    \end{block}
+  }
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Counting events with \mintinline{bash}{perf stat}}
+  { \scriptsize
+    \begin{block}{}
+      \begin{minted}{shell-session}
+$ # Standard CPU counter statistics for the specified command:
+$ perf stat <command>
+
+$ # Detailed CPU counter statistics for the specified command:
+$ perf stat -d <command>
+$ perf stat -dd <command>
+
+$ # Top-down microarchitecture analysis for the entire system, for 10s:
+$ perf stat -a --topdown -- sleep 10
+
+$ # L1 cache hit rate reported every 1000 ms for the specified command:
+$ perf stat -e L1-dcache-loads,L1-dcache-load-misses -I 1000 <command>
+
+$ # Instruction per cycle and Instruction-level parallelism, for command:
+$ perf stat -M IPC,ILP -- <command>
+
+$ # Measure GFLOPs system-wide, until Ctrl-C is used to stop:
+$ perf stat -M GFLOPs
+
+$ # Measure cycles and instructions 10 times, report results with stddev:
+$ perf stat -e cycles,instructions -r 10 -- <command>
+      \end{minted}
+    \end{block}
+  }
+\end{frame}
+
+
+\begin{frame}[fragile]
+  \frametitle{Recording profiling information with \mintinline{bash}{perf record}}
+  { \scriptsize
+    \begin{block}{}
+      \begin{minted}{shell-session}
+$ # Sample on-CPU functions for the specified command, at 100 Hertz:
+$ perf record -F 100 -- <command>
+
+$ # Sample CPU stack traces (via frame pointers), at 100 Hertz, for 10s:
+$ perf record -F 100 -g -- sleep 10
+
+$ # Sample stack traces for PID using DWARF to unwind stacks, for 10s:
+$ perf record -p <PID> --call-graph=dwarf -- sleep 10
+
+$ # Precise on-CPU user stack traces (no skid) using PEBS (Intel CPUs):
+$ perf record -g -e cycles:up -- <command>
+
+$ # Sample CPU stack traces using Instruction-based sampling (AMD CPUs):
+$ # (Note that you need to use system-wide sampling for IBS on AMD CPUs)
+$ perf record -a -g -e cycles:pp -- <command>
+
+$ # Sample CPU stack traces once every 10k L1 data cache misses, for 5s:
+$ perf record -a -g -e L1-dcache-load-misses -c 10000 -- sleep 5
+
+$ # Sample CPUs at 100 Hertz, and show top addresses and symbols, live:
+$ perf top -F 100
+      \end{minted}
+    \end{block}
+  }
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Reporting and annotating source code with \mintinline{bash}{perf}}
+  { \scriptsize
+    \begin{block}{}
+      \begin{minted}{shell-session}
+$ # Standard reporting of perf.data in text UI interface:
+$ perf report
+
+$ # Report by self-time (excluding time spent in callees):
+$ perf report --no-children
+
+$ # Report per source line of code (needs debugging info to work):
+$ perf report --no-children -s srcline
+
+$ # Single inverted (caller-based) call-graph per binary:
+$ perf report --inverted -s comm
+
+$ # Text-based report per library, without call graph:
+$ perf report --stdio -g none -s dso
+
+$ # Hierarchical report for functions taking at least 1% of runtime:
+$ perf report --stdio -g none --hierarchy --percent-limit 1
+
+$ # Disassemble and annotate a symbol (instructions with percentages):
+$ # (Needs debugging information available to show source code as well)
+$ perf annotate <symbol>
+      \end{minted}
+    \end{block}
+  }
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Further information on \mintinline{bash}{perf}}
+  \begin{itemize}
+    \item Official documentation in the Linux repository at
+    \href{https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/Documentation}
+         {linux/tools/perf/Documentation}
+    \item Perf Wiki at \url{https://perf.wiki.kernel.org/}
+    \item Linux \mintinline{bash}{perf} examples by Brendan Gregg
+          \url{https://www.brendangregg.com/linuxperf.html}
+    \item Scripts to visualize profiles as flamegraphs
+          \url{https://github.com/brendangregg/FlameGraph}
+    \item HSF Tools \& Packaging Working Group talk on Indico\\
+          \href{https://indico.cern.ch/event/974382/}
+          {Linux Systems Performance: Tracing, Profiling \& Visualization}
+  \end{itemize}
+\end{frame}
+
+\begin{frame}[fragile]
+  \frametitle{Intel VTune Profiler}
+  \centering
+  \includegraphics[width=0.75\textwidth]{tools/vtune.png}
+  \begin{itemize}
+    \item Very powerful GUI-based profiler for Intel CPUs and GPUs
+    \item Now free to use with
+      \href{https://www.intel.com/content/www/us/en/developer/tools/oneapi/toolkits.html}{Intel oneAPI Base Toolkit} or
+      \href{https://www.intel.com/content/www/us/en/developer/tools/oneapi/vtune-profiler.html}{standalone}
+    \item See the \href{https://www.intel.com/content/www/us/en/develop/documentation/vtune-help/}
+                       {official online documentation} for more information
+  \end{itemize}
 \end{frame}