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REVISION SUMMARY As previously done in other topics, the Rust version is used if it's been built. The version fully in Rust of the partialdiscovery class has the performance advantage over the Python version (actually using the Rust MissingAncestor) if the undecided set is big enough. Otherwise no sampling occurs, and the discovery is reasonably fast anyway. Note: it's hard to predict the size of the initial undecided set, it can depend on the kind of topological changes between the local and remote graphs. The point of the Rust version is to make the bad cases acceptable. More specifically, the performance advantages are: - faster sampling, especially takefullsample() - much faster addmissings() in almost all cases (see commit message in grandparent of the present changeset) - no conversion cost of the undecided set at the interface between Rust and Python Measurements with big undecided sets ------------------------------------ For an extreme example, discovery between mozilla-try and mozilla-unified (over one million undecided revisions, same case as in https://phab.mercurial-scm.org/rHGdbd0fcca6dfca3b0b90ee7c1af30b0a0765e5ea5), we get roughly a x3 better performance: Growing sample size (5%): time goes down from 210 to 72 seconds. Constant sample size: time down from 1853 to 659 seconds. Measurements with small undecided sets -------------------------------------- In cases the undecided set is small enough than no sampling occurs, the Rust version has a disadvantage at init if `targetheads` is really big (some time is lost in the translation to Rust data structures), and that is compensated by the faster `addmissings()`. On a private repository with over one million commits, we still get a minor improvement, of 6.8%: Before ! wall 0.593585 comb 0.590000 user 0.550000 sys 0.040000 (median of 50) After ! wall 0.553035 comb 0.550000 user 0.520000 sys 0.030000 (median of 50) What's interesting in that case is the first addinfo() at 180ms for Rust and 233ms for Python+C, mostly due to add_missings and the children cache computation being done in less than 0.2ms on the Rust side vs over 40ms on the Python side. The worst case we have on hand is with mozilla-try, prepared with discovery-helper.sh for 10 heads and depth 10, time goes up 2.2% on the median. In this case `targetheads` is really huge with 165842 server heads. Before ! wall 0.823884 comb 0.810000 user 0.790000 sys 0.020000 (median of 50) After ! wall 0.842607 comb 0.840000 user 0.800000 sys 0.040000 (median of 50) If that would be considered a problem, more adjustments can be made, which are prematurate at this stage: cooking special variants of methods of the inner MissingAncestors object, retrieving local heads directly from Rust to avoid the cost of conversion. Effort would probably be better spent at this point improving the surroundings if needed. Here's another data point with a smaller repository, pypy, where performance is almost identical Before ! wall 0.015121 comb 0.030000 user 0.020000 sys 0.010000 (median of 186) After ! wall 0.015009 comb 0.010000 user 0.010000 sys 0.000000 (median of 184) REPOSITORY rHG Mercurial REVISION DETAIL https://phab.mercurial-scm.org/D6430 AFFECTED FILES mercurial/setdiscovery.py CHANGE DETAILS diff --git a/mercurial/setdiscovery.py b/mercurial/setdiscovery.py --- a/mercurial/setdiscovery.py +++ b/mercurial/setdiscovery.py @@ -46,6 +46,11 @@ import random from .i18n import _ +try: + from .rustext import discovery as rustdisco +except ImportError: + rustdisco = None + from .node import ( nullid, nullrev, @@ -388,8 +393,11 @@ # full blown discovery randomize = ui.configbool('devel', 'discovery.randomize') - disco = partialdiscovery(local, ownheads, randomize=randomize) - + if rustdisco is not None: + disco = rustdisco.PartialDiscovery(local.changelog.index, ownheads, + randomize=randomize) + else: + disco = partialdiscovery(local, ownheads, randomize=randomize) # treat remote heads (and maybe own heads) as a first implicit sample # response disco.addcommons(knownsrvheads) To: gracinet, #hg-reviewers Cc: mercurial-devel _______________________________________________ Mercurial-devel mailing list Mercurial-devel@mercurial-scm.org https://www.mercurial-scm.org/mailman/listinfo/mercurial-devel
