bundle2: inline changegroup.readexactly() Profiling reveals this loop is pretty tight. Literally any function call elimination can make a big difference. This commit inlines the relatively trivial changegroup.readexactly() method inside the loop. The results with `hg perfbundleread` on a bundle of the Firefox repo speak for themselves: ! read(8k) ! wall 0.679730 comb 0.680000 user 0.140000 sys 0.540000 (best of 15) ! read(16k) ! wall 0.577228 comb 0.570000 user 0.080000 sys 0.490000 (best of 17) ! read(32k) ! wall 0.516060 comb 0.520000 user 0.040000 sys 0.480000 (best of 20) ! read(128k) ! wall 0.496378 comb 0.490000 user 0.010000 sys 0.480000 (best of 20) ! bundle2 iterparts() ! wall 3.460903 comb 3.460000 user 2.760000 sys 0.700000 (best of 3) ! wall 3.056811 comb 3.050000 user 2.340000 sys 0.710000 (best of 4) ! bundle2 iterparts() seekable ! wall 4.312722 comb 4.310000 user 3.480000 sys 0.830000 (best of 3) ! wall 4.007676 comb 4.000000 user 3.170000 sys 0.830000 (best of 3) ! bundle2 part seek() ! wall 6.754764 comb 6.740000 user 3.970000 sys 2.770000 (best of 3) ! wall 6.267110 comb 6.250000 user 3.480000 sys 2.770000 (best of 3) ! bundle2 part read(8k) ! wall 3.668004 comb 3.660000 user 2.960000 sys 0.700000 (best of 3) ! wall 3.404164 comb 3.400000 user 2.650000 sys 0.750000 (best of 3) ! bundle2 part read(16k) ! wall 3.489196 comb 3.480000 user 2.750000 sys 0.730000 (best of 3) ! wall 3.197972 comb 3.200000 user 2.490000 sys 0.710000 (best of 4) ! bundle2 part read(32k) ! wall 3.388569 comb 3.380000 user 2.640000 sys 0.740000 (best of 3) ! wall 3.060557 comb 3.060000 user 2.340000 sys 0.720000 (best of 4) ! bundle2 part read(128k) ! wall 3.276415 comb 3.270000 user 2.560000 sys 0.710000 (best of 4) ! wall 2.952209 comb 2.950000 user 2.230000 sys 0.720000 (best of 4) Differential Revision: https://phab.mercurial-scm.org/D1392

bundle2: inline debug logging Profiling revealed that repeated calls to indebug() were consuming a fair amount of CPU during bundle2 reading, with most of the time spent in ui.configbool(). Inlining indebug() and avoiding extra attribute lookups speeds things up substantially. Using `hg perfbundleread` with a Firefox bundle: ! read(8k) ! wall 0.679730 comb 0.680000 user 0.140000 sys 0.540000 (best of 15) ! read(16k) ! wall 0.577228 comb 0.570000 user 0.080000 sys 0.490000 (best of 17) ! read(32k) ! wall 0.516060 comb 0.520000 user 0.040000 sys 0.480000 (best of 20) ! read(128k) ! wall 0.496378 comb 0.490000 user 0.010000 sys 0.480000 (best of 20) ! bundle2 iterparts() ! wall 6.983756 comb 6.980000 user 6.220000 sys 0.760000 (best of 3) ! wall 3.460903 comb 3.460000 user 2.760000 sys 0.700000 (best of 3) ! bundle2 iterparts() seekable ! wall 8.132131 comb 8.110000 user 7.160000 sys 0.950000 (best of 3) ! wall 4.312722 comb 4.310000 user 3.480000 sys 0.830000 (best of 3) ! bundle2 part seek() ! wall 10.860942 comb 10.840000 user 7.790000 sys 3.050000 (best of 3) ! wall 6.754764 comb 6.740000 user 3.970000 sys 2.770000 (best of 3) ! bundle2 part read(8k) ! wall 7.258035 comb 7.260000 user 6.470000 sys 0.790000 (best of 3) ! wall 3.668004 comb 3.660000 user 2.960000 sys 0.700000 (best of 3) ! bundle2 part read(16k) ! wall 7.099891 comb 7.080000 user 6.310000 sys 0.770000 (best of 3) ! wall 3.489196 comb 3.480000 user 2.750000 sys 0.730000 (best of 3) ! bundle2 part read(32k) ! wall 6.964685 comb 6.950000 user 6.130000 sys 0.820000 (best of 3) ! wall 3.388569 comb 3.380000 user 2.640000 sys 0.740000 (best of 3) ! bundle2 part read(128k) ! wall 6.852867 comb 6.850000 user 6.060000 sys 0.790000 (best of 3) ! wall 3.276415 comb 3.270000 user 2.560000 sys 0.710000 (best of 4) Differential Revision: https://phab.mercurial-scm.org/D1391

bundle2: don't use seekable bundle2 parts by default (issue5691) The last commit removed the last use of the bundle2 part seek() API in the generic bundle2 part iteration code. This means we can now switch to using unseekable bundle2 parts by default and have the special consumers that actually need the behavior request it. This commit changes unbundle20.iterparts() to expose non-seekable unbundlepart instances by default. If seekable parts are needed, callers can pass "seekable=True." The bundlerepo class needs seekable parts, so it does this. The interrupt handler is also changed to use a regular unbundlepart. So, by default, all consumers except bundlerepo will see unseekable parts. Because the behavior of the iterparts() benchmark changed, we add a variation to test seekable parts vs unseekable parts. And because parts no longer have seek() unless "seekable=True," we update the "part seek" benchmark. Speaking of benchmarks, this change has the following impact to `hg perfbundleread` on an uncompressed bundle of the Firefox repo (6,070,036,163 bytes): ! read(8k) ! wall 0.722709 comb 0.720000 user 0.150000 sys 0.570000 (best of 14) ! read(16k) ! wall 0.602208 comb 0.590000 user 0.080000 sys 0.510000 (best of 17) ! read(32k) ! wall 0.554018 comb 0.560000 user 0.050000 sys 0.510000 (best of 18) ! read(128k) ! wall 0.520086 comb 0.530000 user 0.020000 sys 0.510000 (best of 20) ! bundle2 forwardchunks() ! wall 2.996329 comb 3.000000 user 2.300000 sys 0.700000 (best of 4) ! bundle2 iterparts() ! wall 8.070791 comb 8.060000 user 7.180000 sys 0.880000 (best of 3) ! wall 6.983756 comb 6.980000 user 6.220000 sys 0.760000 (best of 3) ! bundle2 iterparts() seekable ! wall 8.132131 comb 8.110000 user 7.160000 sys 0.950000 (best of 3) ! bundle2 part seek() ! wall 10.370142 comb 10.350000 user 7.430000 sys 2.920000 (best of 3) ! wall 10.860942 comb 10.840000 user 7.790000 sys 3.050000 (best of 3) ! bundle2 part read(8k) ! wall 8.599892 comb 8.580000 user 7.720000 sys 0.860000 (best of 3) ! wall 7.258035 comb 7.260000 user 6.470000 sys 0.790000 (best of 3) ! bundle2 part read(16k) ! wall 8.265361 comb 8.250000 user 7.360000 sys 0.890000 (best of 3) ! wall 7.099891 comb 7.080000 user 6.310000 sys 0.770000 (best of 3) ! bundle2 part read(32k) ! wall 8.290308 comb 8.280000 user 7.330000 sys 0.950000 (best of 3) ! wall 6.964685 comb 6.950000 user 6.130000 sys 0.820000 (best of 3) ! bundle2 part read(128k) ! wall 8.204900 comb 8.150000 user 7.210000 sys 0.940000 (best of 3) ! wall 6.852867 comb 6.850000 user 6.060000 sys 0.790000 (best of 3) The significant speedup is due to not incurring the overhead to track payload offset data. Of course, this overhead is proportional to bundle2 part size. So a multiple gigabyte changegroup part is on the extreme side of the spectrum for real-world impact. In addition to the CPU efficiency wins, not tracking offset data also means not using memory to hold that data. Using a bundle based on the example BSD repository in issue 5691, this change has a drastic impact to memory usage during `hg unbundle` (`hg clone` would behave similarly). Before, memory usage incrementally increased for the duration of bundle processing. In other words, as we advanced through the changegroup and bundle2 part, we kept allocating more memory to hold offset data. After this change, we still increase memory during changegroup application. But the rate of increase is significantly slower. (A bulk of the remaining gradual increase appears to be the storing of revlog sizes in the transaction object to facilitate rollback.) The RSS at the end of filelog application is as follows: Before: ~752 MB After: ~567 MB So, we were storing ~185 MB of offset data that we never even used. Talk about wasteful! .. api:: bundle2 parts are no longer seekable by default. .. perf:: bundle2 read I/O throughput significantly increased. .. perf:: Significant memory use reductions when reading from bundle2 bundles. On the BSD repository, peak RSS during changegroup application decreased by ~185 MB from ~752 MB to ~567 MB. Differential Revision: https://phab.mercurial-scm.org/D1390

bundle2: only seek to beginning of part in bundlerepo For reasons still not yet fully understood by me, bundlerepo requires its changegroup bundle2 part to be seeked to beginning after part iteration. As far as I can tell, it is the only bundle2 part consumer that relies on this behavior. This seeking was performed in the generic iterparts() API. Again, I don't fully understand why it was here and not in bundlerepo. Probably historical reasons. What I do know is that all other bundle2 part consumers don't need this special behavior (assuming the tests are comprehensive). So, we move the code from bundle2's iterparts() to bundlerepo's consumption of iterparts(). Differential Revision: https://phab.mercurial-scm.org/D1389

bundle2: implement consume() API on unbundlepart We want bundle parts to not be seekable by default. That means eliminating the generic seek() method. A common pattern in bundle2.py is to seek to the end of the part data. This is mainly used by the part iteration code to ensure the underlying stream is advanced to the next bundle part. In this commit, we establish a dedicated API for consuming a bundle2 part data. We switch users of seek() to it. The old implementation of seek(0, os.SEEK_END) would effectively call self.read(). The new implementation calls self.read(32768) in a loop. The old implementation would therefore assemble a buffer to hold all remaining data being seeked over. For seeking over large bundle parts, this would involve a large allocation and a lot of overhead to collect intermediate data! This overhead can be seen in the results for `hg perfbundleread`: ! bundle2 iterparts() ! wall 10.891305 comb 10.820000 user 7.990000 sys 2.830000 (best of 3) ! wall 8.070791 comb 8.060000 user 7.180000 sys 0.880000 (best of 3) ! bundle2 part seek() ! wall 12.991478 comb 10.390000 user 7.720000 sys 2.670000 (best of 3) ! wall 10.370142 comb 10.350000 user 7.430000 sys 2.920000 (best of 3) Of course, skipping over large payload data isn't likely very common. So I doubt the performance wins will be observed in the wild. Differential Revision: https://phab.mercurial-scm.org/D1388

bundle2: implement generic part payload decoder The previous commit extracted _payloadchunks() to a new derived class. There was still a reference to this method in unbundlepart, making unbundlepart unusable on its own. This commit implements a generic version of a bundle2 part payload decoder, without offset tracking. seekableunbundlepart._payloadchunks() has been refactored to consume it, adding offset tracking like before. We also implement unbundlepart._payloadchunks(), which is a thin wrapper for it. Since we never instantiate unbundlepart directly, this new method is not used. This will be changed in subsequent commits. The new implementation also inlines some simple code from unpackermixin and adds some local variable to prevent extra function calls and attribute lookups. `hg perfbundleread` on an uncompressed Firefox bundle seems to show a minor win: ! bundle2 iterparts() ! wall 12.593258 comb 12.250000 user 8.870000 sys 3.380000 (best of 3) ! wall 10.891305 comb 10.820000 user 7.990000 sys 2.830000 (best of 3) ! bundle2 part seek() ! wall 13.173163 comb 11.100000 user 8.390000 sys 2.710000 (best of 3) ! wall 12.991478 comb 10.390000 user 7.720000 sys 2.670000 (best of 3) ! bundle2 part read(8k) ! wall 9.483612 comb 9.480000 user 8.420000 sys 1.060000 (best of 3) ! wall 8.599892 comb 8.580000 user 7.720000 sys 0.860000 (best of 3) ! bundle2 part read(16k) ! wall 9.159815 comb 9.150000 user 8.220000 sys 0.930000 (best of 3) ! wall 8.265361 comb 8.250000 user 7.360000 sys 0.890000 (best of 3) ! bundle2 part read(32k) ! wall 9.141308 comb 9.130000 user 8.220000 sys 0.910000 (best of 3) ! wall 8.290308 comb 8.280000 user 7.330000 sys 0.950000 (best of 3) ! bundle2 part read(128k) ! wall 8.880587 comb 8.850000 user 7.960000 sys 0.890000 (best of 3) ! wall 8.204900 comb 8.150000 user 7.210000 sys 0.940000 (best of 3) Function call overhead in Python strikes again! Of course, bundle2 decoding CPU overhead is likely small compared to decompression and changegroup application. But every little bit helps. Differential Revision: https://phab.mercurial-scm.org/D1387