perf: add command for measuring revlog chunk operations

perf: add command for measuring revlog chunk operations

Upcoming commits will teach revlogs to leverage the new compression
engine API so that new compression formats can more easily be
leveraged in revlogs. We want to be sure this refactoring doesn't
regress performance. So this commit introduces "perfrevchunks" to
explicitly test performance of reading, decompressing, and
recompressing revlog chunks.

Here is output when run on the mozilla-unified repo:

$ hg perfrevlogchunks -c
! read
! wall 0.346603 comb 0.350000 user 0.340000 sys 0.010000 (best of 28)
! read w/ reused fd
! wall 0.337707 comb 0.340000 user 0.320000 sys 0.020000 (best of 30)
! read batch
! wall 0.013206 comb 0.020000 user 0.000000 sys 0.020000 (best of 221)
! read batch w/ reused fd
! wall 0.013259 comb 0.030000 user 0.010000 sys 0.020000 (best of 222)
! chunk
! wall 1.909939 comb 1.910000 user 1.900000 sys 0.010000 (best of 6)
! chunk batch
! wall 1.750677 comb 1.760000 user 1.740000 sys 0.020000 (best of 6)
! compress
! wall 5.668004 comb 5.670000 user 5.670000 sys 0.000000 (best of 3)

$ hg perfrevlogchunks -m
! read
! wall 0.365834 comb 0.370000 user 0.350000 sys 0.020000 (best of 26)
! read w/ reused fd
! wall 0.350160 comb 0.350000 user 0.320000 sys 0.030000 (best of 28)
! read batch
! wall 0.024777 comb 0.020000 user 0.000000 sys 0.020000 (best of 119)
! read batch w/ reused fd
! wall 0.024895 comb 0.030000 user 0.000000 sys 0.030000 (best of 118)
! chunk
! wall 2.514061 comb 2.520000 user 2.480000 sys 0.040000 (best of 4)
! chunk batch
! wall 2.380788 comb 2.380000 user 2.360000 sys 0.020000 (best of 5)
! compress
! wall 9.815297 comb 9.820000 user 9.820000 sys 0.000000 (best of 3)

We already see some interesting data, such as how much slower
non-batched chunk reading is and that zlib compression appears to be
>2x slower than decompression.

I didn't have the data when I wrote this commit message, but I ran this
on Mozilla's NFS-based Mercurial server and the time for reading with a
reused file descriptor was faster. So I think it is worth testing both
with and without file descriptor reuse so we can make informed
decisions about recycling file descriptors.

--- a/contrib/perf.py	Thu Nov 17 20:09:10 2016 -0800
+++ b/contrib/perf.py	Thu Nov 17 20:17:51 2016 -0800
@@ -859,6 +859,84 @@
     timer(d)
     fm.end()
 
+@command('perfrevlogchunks', revlogopts + formatteropts +
+         [('s', 'startrev', 0, 'revision to start at')],
+         '-c|-m|FILE')
+def perfrevlogchunks(ui, repo, file_=None, startrev=0, **opts):
+    """Benchmark operations on revlog chunks.
+
+    Logically, each revlog is a collection of fulltext revisions. However,
+    stored within each revlog are "chunks" of possibly compressed data. This
+    data needs to be read and decompressed or compressed and written.
+
+    This command measures the time it takes to read+decompress and recompress
+    chunks in a revlog. It effectively isolates I/O and compression performance.
+    For measurements of higher-level operations like resolving revisions,
+    see ``perfrevlog`` and ``perfrevlogrevision``.
+    """
+    rl = cmdutil.openrevlog(repo, 'perfrevlogchunks', file_, opts)
+    revs = list(rl.revs(startrev, len(rl) - 1))
+
+    def rlfh(rl):
+        if rl._inline:
+            return getsvfs(repo)(rl.indexfile)
+        else:
+            return getsvfs(repo)(rl.datafile)
+
+    def doread():
+        rl.clearcaches()
+        for rev in revs:
+            rl._chunkraw(rev, rev)
+
+    def doreadcachedfh():
+        rl.clearcaches()
+        fh = rlfh(rl)
+        for rev in revs:
+            rl._chunkraw(rev, rev, df=fh)
+
+    def doreadbatch():
+        rl.clearcaches()
+        rl._chunkraw(revs[0], revs[-1])
+
+    def doreadbatchcachedfh():
+        rl.clearcaches()
+        fh = rlfh(rl)
+        rl._chunkraw(revs[0], revs[-1], df=fh)
+
+    def dochunk():
+        rl.clearcaches()
+        fh = rlfh(rl)
+        for rev in revs:
+            rl._chunk(rev, df=fh)
+
+    chunks = [None]
+
+    def dochunkbatch():
+        rl.clearcaches()
+        fh = rlfh(rl)
+        # Save chunks as a side-effect.
+        chunks[0] = rl._chunks(revs, df=fh)
+
+    def docompress():
+        rl.clearcaches()
+        for chunk in chunks[0]:
+            rl.compress(chunk)
+
+    benches = [
+        (lambda: doread(), 'read'),
+        (lambda: doreadcachedfh(), 'read w/ reused fd'),
+        (lambda: doreadbatch(), 'read batch'),
+        (lambda: doreadbatchcachedfh(), 'read batch w/ reused fd'),
+        (lambda: dochunk(), 'chunk'),
+        (lambda: dochunkbatch(), 'chunk batch'),
+        (lambda: docompress(), 'compress'),
+    ]
+
+    for fn, title in benches:
+        timer, fm = gettimer(ui, opts)
+        timer(fn, title=title)
+        fm.end()
+
 @command('perfrevlogrevision', revlogopts + formatteropts +
          [('', 'cache', False, 'use caches instead of clearing')],
          '-c|-m|FILE REV')

--- a/tests/test-contrib-perf.t	Thu Nov 17 20:09:10 2016 -0800
+++ b/tests/test-contrib-perf.t	Thu Nov 17 20:17:51 2016 -0800
@@ -95,6 +95,8 @@
                  (no help text available)
    perfrawfiles  (no help text available)
    perfrevlog    Benchmark reading a series of revisions from a revlog.
+   perfrevlogchunks
+                 Benchmark operations on revlog chunks.
    perfrevlogrevision
                  Benchmark obtaining a revlog revision.
    perfrevrange  (no help text available)
@@ -144,6 +146,7 @@
   $ hg perfrawfiles 2
   $ hg perfrevlog .hg/store/data/a.i
   $ hg perfrevlogrevision -m 0
+  $ hg perfrevlogchunks -c
   $ hg perfrevrange
   $ hg perfrevset 'all()'
   $ hg perfstartup