revsetbenchmarks: clarify comment based on irc discussion

contrib/revsetbenchmarks.py

@@ -1,200 +1,203
 #!/usr/bin/env python
 
 # Measure the performance of a list of revsets against multiple revisions
 # defined by parameter. Checkout one by one and run perfrevset with every
 # revset in the list to benchmark its performance.
 #
 # - First argument is a revset of mercurial own repo to runs against.
 # - Second argument is the file from which the revset array will be taken
 #   If second argument is omitted read it from standard input
 #
 # You should run this from the root of your mercurial repository.
 #
 # This script also does one run of the current version of mercurial installed
 # to compare performance.
 
 import sys
 import os
 import re
 from subprocess import check_call, Popen, CalledProcessError, STDOUT, PIPE
 # cannot use argparse, python 2.7 only
 from optparse import OptionParser
 
 def check_output(*args, **kwargs):
     kwargs.setdefault('stderr', PIPE)
     kwargs.setdefault('stdout', PIPE)
     proc = Popen(*args, **kwargs)
     output, error = proc.communicate()
     if proc.returncode != 0:
         raise CalledProcessError(proc.returncode, ' '.join(args[0]))
     return output
 
 def update(rev):
     """update the repo to a revision"""
     try:
         check_call(['hg', 'update', '--quiet', '--check', str(rev)])
     except CalledProcessError, exc:
         print >> sys.stderr, 'update to revision %s failed, aborting' % rev
         sys.exit(exc.returncode)
 
 
 def hg(cmd, repo=None):
     """run a mercurial command
 
     <cmd> is the list of command + argument,
     <repo> is an optional repository path to run this command in."""
     fullcmd = ['./hg']
     if repo is not None:
         fullcmd += ['-R', repo]
     fullcmd += ['--config',
                 'extensions.perf=' + os.path.join(contribdir, 'perf.py')]
     fullcmd += cmd
     return check_output(fullcmd, stderr=STDOUT)
 
 def perf(revset, target=None):
     """run benchmark for this very revset"""
     try:
         output = hg(['perfrevset', revset], repo=target)
         return parseoutput(output)
     except CalledProcessError, exc:
         print >> sys.stderr, 'abort: cannot run revset benchmark: %s' % exc.cmd
         if exc.output is None:
             print >> sys.stderr, '(no ouput)'
         else:
             print >> sys.stderr, exc.output
         sys.exit(exc.returncode)
 
 outputre = re.compile(r'! wall (\d+.\d+) comb (\d+.\d+) user (\d+.\d+) '
                       'sys (\d+.\d+) \(best of (\d+)\)')
 
 def parseoutput(output):
     """parse a textual output into a dict
 
     We cannot just use json because we want to compare with old
     versions of Mercurial that may not support json output.
     """
     match = outputre.search(output)
     if not match:
         print >> sys.stderr, 'abort: invalid output:'
         print >> sys.stderr, output
         sys.exit(1)
     return {'comb': float(match.group(2)),
             'count': int(match.group(5)),
             'sys': float(match.group(3)),
             'user': float(match.group(4)),
             'wall': float(match.group(1)),
             }
 
 def printrevision(rev):
     """print data about a revision"""
     sys.stdout.write("Revision: ")
     sys.stdout.flush()
     check_call(['hg', 'log', '--rev', str(rev), '--template',
                '{desc|firstline}\n'])
 
 def idxwidth(nbidx):
     """return the max width of number used for index
 
-    Yes, this is basically a log10."""
+    This is similar to log10(nbidx), but we use custom code here
+    because we start with zero and we'd rather not deal with all the
+    extra rounding business that log10 would imply.
+    """
     nbidx -= 1 # starts at 0
     idxwidth = 0
     while nbidx:
         idxwidth += 1
         nbidx //= 10
     if not idxwidth:
         idxwidth = 1
     return idxwidth
 
 def printresult(idx, data, maxidx):
     """print a line of result to stdout"""
     mask = '%%0%ii) %%s' % idxwidth(maxidx)
 
     out = ("wall %f comb %f user %f sys %f (best of %d)"
            % (data['wall'], data['comb'], data['user'],
               data['sys'], data['count']))
 
     print mask % (idx, out)
 
 def getrevs(spec):
     """get the list of rev matched by a revset"""
     try:
         out = check_output(['hg', 'log', '--template={rev}\n', '--rev', spec])
     except CalledProcessError, exc:
         print >> sys.stderr, "abort, can't get revision from %s" % spec
         sys.exit(exc.returncode)
     return [r for r in out.split() if r]
 
 
 parser = OptionParser(usage="usage: %prog [options] <revs>")
 parser.add_option("-f", "--file",
                   help="read revset from FILE (stdin if omitted)",
                   metavar="FILE")
 parser.add_option("-R", "--repo",
                   help="run benchmark on REPO", metavar="REPO")
 
 (options, args) = parser.parse_args()
 
 if len(sys.argv) < 2:
     parser.print_help()
     sys.exit(255)
 
 # the directory where both this script and the perf.py extension live.
 contribdir = os.path.dirname(__file__)
 
 target_rev = args[0]
 
 revsetsfile = sys.stdin
 if options.file:
     revsetsfile = open(options.file)
 
 revsets = [l.strip() for l in revsetsfile if not l.startswith('#')]
 
 print "Revsets to benchmark"
 print "----------------------------"
 
 for idx, rset in enumerate(revsets):
     print "%i) %s" % (idx, rset)
 
 print "----------------------------"
 print
 
 
 revs = getrevs(target_rev)
 
 results = []
 for r in revs:
     print "----------------------------"
     printrevision(r)
     print "----------------------------"
     update(r)
     res = []
     results.append(res)
     for idx, rset in enumerate(revsets):
         data = perf(rset, target=options.repo)
         res.append(data)
         printresult(idx, data, len(revsets))
         sys.stdout.flush()
     print "----------------------------"
 
 
 print """
 
 Result by revset
 ================
 """
 
 print 'Revision:', revs
 for idx, rev in enumerate(revs):
     sys.stdout.write('%i) ' % idx)
     sys.stdout.flush()
     printrevision(rev)
 
 print
 print
 
 for ridx, rset in enumerate(revsets):
 
     print "revset #%i: %s" % (ridx, rset)
     for idx, data in enumerate(results):
         printresult(idx, data[ridx], len(results))
     print