Recherche avancée

Sur d’autres sites (4366)

• Monster Battery Power Revisited

  28 mai 2010, par Multimedia Mike — Python, Science Projects

  So I have this new fat netbook battery and I performed an experiment to determine how long it really lasts. In my last post on the matter, it was suggested that I should rely on the information that gnome-power-manager is giving me. However, I have rarely seen GPM report more than about 2 hours of charge ; even on a full battery, it only reports 3h25m when I profiled it as lasting over 5 hours in my typical use. So I started digging to understand how GPM gets its numbers and determine if, perhaps, it’s not getting accurate data from the system.

  I started poking around /proc for the data I wanted. You can learn a lot in /proc as long as you know the right question to ask. I had to remember what the power subsystem is called — ACPI — and this led me to /proc/acpi/battery/BAT0/state which has data such as :

  present :                 yes
  capacity state :          ok
  charging state :          charged
  present rate :            unknown
  remaining capacity :      100 mAh
  present voltage :         8326 mV
  

  "Remaining capacity" rated in mAh is a little odd ; I would later determine that this should actually be expressed as a percentage (i.e., 100% charge at the time of this reading). Examining the GPM source code, it seems to determine as a function of the current CPU load (queried via /proc/stat) and the battery state queried via a facility called devicekit. I couldn’t immediately find any source code to the latter but I was able to install a utility called ’devkit-power’. Mostly, it appears to rehash data already found in the above /proc file.

  Curiously, the file /proc/acpi/battery/BAT0/info, which displays essential information about the battery, reports the design capacity of my battery as only 4400 mAh which is true for the original battery ; the new monster battery is supposed to be 10400 mAh. I can imagine that all of these data points could be conspiring to under-report my remaining battery life.

  Science project : Repeat the previous power-related science project but also parse and track the remaining capacity and present voltage fields from the battery state proc file.

  Let’s skip straight to the results (which are consistent with my last set of results in terms of longevity) :

  
  
  

  So there is definitely something strange going on with the reporting— the 4400 mAh battery reports discharge at a linear rate while the 10400 mAh battery reports precipitous dropoff after 60%.

  Another curious item is that my script broke at first when there was 20% power remaining which, as you can imagine, is a really annoying time to discover such a bug. At that point, the "time to empty" reported by devkit-power jumped from 0 seconds to 20 hours (the first state change observed for that field).

  Here’s my script, this time elevated from Bash script to Python. It requires xdotool and devkit-power to be installed (both should be available in the package manager for a distro).
  

  PLAIN TEXT

  PYTHON :

  1. # !/usr/bin/python
  2.  
  3. import commands
  4. import random
  5. import sys
  6. import time
  7.  
  8. XDOTOOL = "/usr/bin/xdotool"
  9. BATTERY_STATE = "/proc/acpi/battery/BAT0/state"
  10. DEVKIT_POWER = "/usr/bin/devkit-power -i /org/freedesktop/DeviceKit/Power/devices/battery_BAT0"
  11.  
  12. print "count, unixtime, proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage"
  13.  
  14. count = 0
  15. while 1 :
  16.   commands.getstatusoutput("%s mousemove %d %d" % (XDOTOOL, random.randrange(0,800), random.randrange(0, 480)))
  17.   battery_state = open(BATTERY_STATE).read().splitlines()
  18.   for line in battery_state :
  19.     if line.startswith("remaining capacity :") :
  20.       proc_remaining_capacity = int(line.lstrip("remaining capacity : ").rstrip("mAh"))
  21.     elif line.startswith("present voltage :") :
  22.       proc_present_voltage = int(line.lstrip("present voltage : ").rstrip("mV"))
  23.   devkit_state = commands.getoutput(DEVKIT_POWER).splitlines()
  24.   for line in devkit_state :
  25.     line = line.strip()
  26.     if line.startswith("percentage :") :
  27.       devkit_percentage = int(line.lstrip("percentage :").rstrip(’\%’))
  28.     elif line.startswith("voltage :") :
  29.       devkit_voltage = float(line.lstrip("voltage :").rstrip(’V’)) * 1000
  30.   print "%d, %d, %d, %d, %d, %d" % (count, time.time(), proc_remaining_capacity, proc_present_voltage, devkit_percentage, devkit_voltage)
  31.   sys.stdout.flush()
  32.   time.sleep(60)
  33.   count += 1

• checkasm : vvc_alf : Limit benchmarking to a reasonable subset of functions

  21 mai 2024, par Martin Storsjö

  checkasm : vvc_alf : Limit benchmarking to a reasonable subset of functions
  Don't benchmark every single combination of widths and heights ;
  
  only benchmark cases which are squares (like in vvc_mc.c).
  Contrary to vvc_mc, which increases sizes by doubling dimensions,
  
  vvc_alf tests all sizes in increments of 4. Limit benchmarking to
  
  the cases which are powers of two.
  This reduces the number of benchmarked cases from 3072 down to 18.
  

  • [DH] tests/checkasm/vvc_alf.c

• FFmpeg and Code Coverage Tools

  21 août 2010, par Multimedia Mike — FATE Server, Python

  Code coverage tools likely occupy the same niche as profiling tools : Tools that you’re supposed to use somewhere during the software engineering process but probably never quite get around to it, usually because you’re too busy adding features or fixing bugs. But there may come a day when you wish to learn how much of your code is actually being exercised in normal production use. For example, the team charged with continuously testing the FFmpeg project, would be curious to know how much code is being exercised, especially since many of the FATE test specs explicitly claim to be "exercising XYZ subsystem".

  The primary GNU code coverage tool is called gcov and is probably already on your GNU-based development system. I set out to determine how much FFmpeg source code is exercised while running the full FATE suite. I ran into some problems when trying to use gcov on a project-wide scale. I spackled around those holes with some very ad-hoc solutions. I’m sure I was just overlooking some more obvious solutions about which you all will be happy to enlighten me.

  Results
  I’ve learned to cut to the chase earlier in blog posts (results first, methods second). With that, here are the results I produced from this experiment. This Google spreadsheet contains 3 sheets : The first contains code coverage stats for a bunch of FFmpeg C files sorted first by percent coverage (ascending), then by number of lines (descending), thus highlighting which files have the most uncovered code (ffserver.c currently tops that chart). The second sheet has files for which no stats were generated. The third sheet has "problems". These files were rejected by my ad-hoc script.

  Here’s a link to the data in CSV if you want to play with it yourself.

  Using gcov with FFmpeg
  To instrument a program for gcov analysis, compile and link the target program with the -fprofile-arcs and -ftest-coverage options. These need to be applied at both the compile and link stages, so in the case of FFmpeg, configure with :

    ./configure \
      —extra-cflags="-fprofile-arcs -ftest-coverage" \
      —extra-ldflags="-fprofile-arcs -ftest-coverage"
  

  The building process results in a bunch of .gcno files which pertain to code coverage. After running the program as normal, a bunch of .gcda files are generated. To get coverage statistics from these files, run 'gcov sourcefile.c'. This will print some basic statistics as well as generate a corresponding .gcov file with more detailed information about exactly which lines have been executed, and how many times.

  Be advised that the source file must either live in the same directory from which gcov is invoked, or else the path to the source must be given to gcov via the '-o, --object-directory' option.

  Resetting Statistics
  Statistics in the .gcda are cumulative. Should you wish to reset the statistics, doing this in the build directory should suffice :

    find . -name "*.gcda" | xargs rm -f
  

  Getting Project-Wide Data
  As mentioned, I had to get a little creative here to get a big picture of FFmpeg code coverage. After building FFmpeg with the code coverage options and running FATE,

  for file in `find . -name "*.c"` \
  do \
    echo "*****" $file \
    gcov -o `dirname $file` `basename $file` \
  done > ffmpeg-code-coverage.txt 2>&1
  

  After that, I ran the ffmpeg-code-coverage.txt file through a custom Python script to print out the 3 CSV files that I later dumped into the Google Spreadsheet.

  Further Work
  I’m sure there are better ways to do this, and I’m sure you all will let me know what they are. But I have to get the ball rolling somehow.

  There’s also TestCocoon. I’d like to try that program and see if it addresses some of gcov’s shortcomings (assuming they are indeed shortcomings rather than oversights).

  Source for script : process-gcov-slop.py

  PLAIN TEXT

  PYTHON :

  1. # !/usr/bin/python
  2.  
  3. import re
  4.  
  5. lines = open("ffmpeg-code-coverage.txt").read().splitlines()
  6. no_coverage = ""
  7. coverage = "filename, % covered, total lines\n"
  8. problems = ""
  9.  
  10. stats_exp = re.compile(’Lines executed :(\d+\.\d+)% of (\d+)’)
  11. for i in xrange(len(lines)) :
  12.   line = lines[i]
  13.   if line.startswith("***** ") :
  14.     filename = line[line.find(’./’)+2 :]
  15.     i += 1
  16.     if lines[i].find(":cannot open graph file") != -1 :
  17.       no_coverage += filename + ’\n’
  18.     else :
  19.       while lines[i].find(filename) == -1 and not lines[i].startswith("***** ") :
  20.         i += 1
  21.       try :
  22.         (percent, total_lines) = stats_exp.findall(lines[i+1])[0]
  23.         coverage += filename + ’, ’ + percent + ’, ’ + total_lines + ’\n’
  24.       except IndexError :
  25.         problems += filename + ’\n’
  26.  
  27. open("no_coverage.csv", ’w’).write(no_coverage)
  28. open("coverage.csv", ’w’).write(coverage)
  29. open("problems.csv", ’w’).write(problems)