Post on 17-Jan-2016
Profiling Tools
Introduction to Computer System, Fall 2015. (PPI, FDU)
Vtune & GProfile
Profiling• In software engineering, profiling ("program profiling",
"software profiling") is a form of dynamic program analysis that measures, for example, the space (memory) or time complexity of a program, the usage of particular instructions, or the frequency and duration of function calls. Most commonly, profiling information serves to aid program optimization.
• Profiling is achieved by instrumenting either the program source code or its binary executable form using a tool called a profiler (or code profiler). Profilers may use a number of different techniques, such as event-based, statistical, instrumented, and simulation methods.
Performance Tuning forIntel® Xeon Phi™ Coprocessors
Visualizing Performance Opportunities using Intel® VTune™ Amplifier
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Introduction
Can profile host, offload or native coprocessor applications
Host-based profiling may be sufficient to identify vectorization/parallelism/ offload candidates Call stacks currently available for host only
Start with representative/reasonable workloads!
Use Intel® VTune™ Amplifier XE to gather hot spot data
Tells what functions account for most of the run time
Often, this is enough
But it does not tell you much about program structure
Move on to more detailed analyses
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Hotspot (Statistical call tree)Hardware-Event Based Sampling
Thread Profiling
Visualize thread interactions on timelineBalance workloads
Easy set-up
Pre-defined performance profilesUse a normal production build
Compatible
Microsoft*, GCC*, Intel compilersC/C++, Fortran, Assembly, .NET*Latest Intel processorsand compatible processors1
Find Answers Fast
Filter out extraneous dataView results tied to source/assembly linesEvent multiplexing
Windows* or Linux*Visual Studio* Integration (Windows)
Standalone user interface and command line32 and 64-bit
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Intel® VTune™ Amplifier XETune Applications for Scalable MulticorePerformance
Fast, Accurate Performance Profiles
1IA-32 and Intel® 64 architectures.Many features work with compatible processors.Event based sampling requires a genuine Intel Processor.
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A Quick Tour Through Intel® VTune™AmplifierSetting up a project
Execution file, command line arguments, working directory
Search directories (standard binary libraries for Intel MPSS 3)
Quick tour of advanced setup dialog
Selecting a collector
Host versus native event collection
Launching a collection
Viewing results, source and assembly
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VTune™ Amplifier XE visualizes performance
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VTune™ Amplifier XE visualizes performance
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Instructions Navigator New New CompareOpenResult
Open PropertiesProject
Toolbar
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VTune™ Amplifier XE visualizes performance
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Grid Pane
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VTune™ Amplifier XE visualizes performance
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Grid Pane
Grouping pull-down
VTune™ Amplifier XE visualizes performance
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Source View /
Per line localization
VTune™ Amplifier XE visualizes performance
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Source View /
View / Hot spotNavigation controls
Can also copy small data files onto card,but will need to be recopied after reboot.
Suggest create /tmp/usrname as workingdirectory
VTune™ Amplifier XE visualizes performance
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Assembly View /
View / Hot spotNavigation controls
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For event collection the coprocessor istreated as a special HW architecture
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General Exploration runs a set of events todrive top-down analysis
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VTune™ Amplifier XE visualizes performance
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Assembly View /
View / Hot spotNavigation controls
VTune™ Amplifier
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Advantage• Both command line and GUI, easy to use
• Multiple predefined analyzing suite
• Support hardware events like cache and memory access analysis
• Multithread profiling well supported
VTune™ Amplifier
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Limitations• For enterprise use, Expensive!!!
• Can only be used on intel machines.
GPROF• Gprof is a performance analysis tool for Unix
applications. It uses a hybrid of instrumentation and sampling and was created as extended version of the older "prof" tool. Unlike prof, gprof is capable of limited call graph collecting and printing.
Usage
• Instrumentation code is automatically inserted into the program code during compilation (for example, by using the '-pg' option of the gcc compiler), to gather caller-function data. A call to the monitor function 'mcount' is inserted before each function call.
• gcc -Wall -g -pg -lc_p example.c -o example• ./example will create gmon.out• gprof -b example gmon.out
Result• Gprof output consists of two parts: the flat profile
and the call graph. The flat profile gives the total execution time spent in each function and its percentage of the total running time. Function call counts are also reported. Output is sorted by percentage, with hot spots at the top of the list.
Result% the percentage of the total running time of thetime program used by this function.
cumulative a running sumof the number of seconds accountedseconds for by this function and those listed above it.
self the number of seconds accounted for by thisseconds function alone. This is the major sort for this listing.
calls the number of times this function was invoked, if this function is profiled, else blank.
self the average number of milliseconds spent in thisms/call function per call, if this function is profiled, else blank.
total the average number of milliseconds spent in thisms/call function and its descendents per call, if this function is profiled, else blank. name the name of the function. This is the minor sort for this listing. The index shows the location of the function in the gprof listing. If the index is in parenthesis it shows where it would appear in the gprof listing if it were to be printed.
Advantages
• GNU is not UNIX(supported by GNU)• Unlimited by hardwares
Limitations
• Gprof cannot measure time spent in kernel mode (syscalls, waiting for CPU or I/O waiting), and only user-space code is profiled.
• Gprof profiles the main thread of application of multi-threaded application.
• Insert code when compiling.• No hardware events.
More
• man gprof• https://sourceware.org/binutils/
docs/gprof/
Open topic
Introduction to Computer System, Fall 2015. (PPI, FDU)
Pwned
Attack: Stack Buffer Overflow• A Typical Buffer Overflow Attack
– Inject malicious code in buffer– Overwrite return address to
buffer– Once return, the malicious code
runs 0110110101010101010101101010101010101010
return addrsaved ebp
ebp
buf
01010110101010111010
void function(char *str) { char buf[16]; strcpy(buf,str);}
Defense: DEP (Data Execution Prevention)
• Execute Code, not Data• Data areas marked non-
executable– Stack marked non-executable
• Hardware enforced (NX)• You can load your shellcode in the
stack …but you can’t jump to it
slide 30
How to pwn?
• Give other ways of pwning except buffer overflow.
• Focusing on how to change the program form its normal execution path.
Debugging
How to Debug?
• The Program gets wrong results• Runs program in debug mode• Execute the code line by line to find
the cause
Can this always work well in a multi-threads program?
If not, why? what’s the difference between sequential bugs and parallel ones?
And how to debug a tricky multi-threads program?
Cache
Cache locality
• Cache locality is the key to achieving high levels of performance.
• We can improve cache locality by either optimizing our program or changing the cache strategy or the implementation.
• You can introduce some methods to improve the cache locality from certain perspective and present how it works.
Requirement
• Each student picks one topic and do a presentation with ppt slides.
• Any techniques or methods if you can finish presentation within 6 min
• 2015/10/30 6-7 classroom will be informed later.
• PPT slides should be emailed to your TA before 2015/10/29 23:59 p.m.
How to score high？• Illustrate your ideas clearly, you may refer to the
Internet or give out your own solution.• Remember time is limited, try to be precise and
concise.• Your presentation contains three part: PPT, oral
speaking and your content. All of these are important in grading.