The performance issues in Ubuntu 14.04 is not surprising. 14.04’s ICU version is ancient, relatively speaking (e.g. it predates both Swift and Unicode 7.0). Performance issues is not the only problem there, as Unicode semantics such as grapheme breaking has evolved dramatically since then. Out of curiosity, is there a reason why Kitura is stuck on 14.04? Can your platform bundle a newer ICU so that your users can have things like modern emoji support?
> On Jul 27, 2017, at 7:28 AM, David Jones via swift-dev <swift-dev@swift.org> > wrote: > > FWIW, here is an illustration of how much an optimization in this area would > be worth to Kitura, running on Ubuntu 14.04 (where ICU 52 is particularly > expensive when comparing ASCII strings [1]). > The workload I used here is https://github.com/tbrand/which_is_the_fastest > <https://github.com/tbrand/which_is_the_fastest> > I have compiled Kitura 1.7.6 with the latest 4.0 toolchain (07-26-a), and > again with the same toolchain modified to remove the #if in StringCompare's > ==. > > djones6@needletail:~/which_is_the_fastest$ numactl --physcpubind=0-3,16-19 > --membind=0 bin/benchmarker kitura_40 kitura_40_memcmp > Language (Runtime) Framework (Middleware) Max [sec] Min > [sec] Ave [sec] > ------------------------- ------------------------- --------------- > --------------- --------------- > swift kitura_40 7.824673 > 7.682657 7.740933 > swift kitura_40_memcmp 5.163788 > 4.811082 4.955571 > > The difference here is around 35%. Other Kitura workloads I've performed this > comparison on in the past (such as involving JSON serialization) have showed > a difference in the 15 - 20% region. > The difference is far smaller on Ubuntu 16.04 (around 8% for this workload), > due to improvements in the newer level of ICU: > > djones6@gruffalo:~/which_is_the_fastest$ numactl --physcpubind=0-3,16-19 > --membind=0 bin/benchmarker kitura_40 kitura_40_memcmp > Language (Runtime) Framework (Middleware) Max [sec] Min > [sec] Ave [sec] > ------------------------- ------------------------- --------------- > --------------- --------------- > swift kitura_40 4.691993 > 4.531465 4.580086 > swift kitura_40_memcmp 4.349387 > 4.015061 4.201105 > > - David. > --- > David Jones, Swift@IBM > > [1] https://github.com/apple/swift/pull/7339 > <https://github.com/apple/swift/pull/7339> > > On 26 July 2017 at 03:59, Michael Ilseman via swift-dev <swift-dev@swift.org > <mailto:swift-dev@swift.org>> wrote: > Unfortunately after some investigations and discussion, the situation seems > to be more murky. This approach would break transitivity of String comparison > on Linux, at least with any implementation of UCA using the normal collation > weights. A < B, B < C should imply A < C. But, if both A and B are > known-ASCII while C is UTF16, transitivity can be broken for any character > that UCA yields a different sort order for (e.g. “#” vs “&”). On Darwin, the > comparison implementation happens to preserve transitivity as the platform > (in effect) relatively weights ASCII by code unit values. > > While I would like to get some performance improvements in time for Linux, I > don’t think this approach is viable for Swift 4.0. Unless anyone has any > ideas about another minimally invasive approach, my recommendation is to do > the long-term solution (lexicographical order of normalized code units) > immediately after Swift 4.0. > > >> On Jul 25, 2017, at 2:01 PM, Michael Ilseman via swift-dev >> <swift-dev@swift.org <mailto:swift-dev@swift.org>> wrote: >> >> On Darwin, known-ASCII strings are sorted according to the lexicographical >> ordering of their code units. All non-known-ASCII strings are otherwise >> ordered based on the UCA[1]. On Linux, however, even known-ASCII strings are >> ordered based on UCA. I propose to unify these by changing Linux’s string >> sort order to match Darwin’s in Swift 4.0. >> >> Background >> >> Swift’s default ordering for strings is appropriate for machine consumption >> (e.g. implementing sorted collections). It obeys Unicode canonical >> equivalence[2], that is strings compare the same modulo normalization. >> However, it is not meant to be sufficient for presenting a meaningful >> ordering to human consumers, as that requires incorporating reader-specific >> information (e.g. [3]). >> >> Known-ASCII strings are a trivial case for the described sort order >> semantics: pure ASCII is unaffected by normalization. Thus, lexicographical >> ordering of code units is a valid machine ordering for ASCII strings. On >> Darwin, this is used to order known-ASCII strings while Linux uses UCA even >> for known-ASCII strings. >> >> Long term, the plan is to switch String’s sort order to be the >> lexicographical ordering of normalized code units (or perhaps scalar >> values), as mentioned in the String Manifesto[4]. This is a more efficient >> ordering than that provided by UCA. However, this will not make it in time >> for Swift 4.0. >> >> Changes >> >> I propose to change Linux’s sort order for known-ASCII strings to be the >> same as it is on Darwin. This will be accomplished by dropping the relevant >> #if guards in StringCompare.swift. An example implementation can be found at >> [5]. >> >> In addition to unifying sort order semantics across platforms, this will >> also deliver significant performance boosts to pure ASCII strings on Linux. >> >> [1] UTS #10: Unicode Collation Algorithm <http://unicode.org/reports/tr10/> >> [2] Canonical Equivalence in Applications <http://unicode.org/notes/tn5/> >> [3] UCA: Contextual Sensitivity >> <http://unicode.org/reports/tr10/#Contextual_Sensitivity> >> [4] String Manifesto: Comparing and Hashing Strings >> <https://github.com/apple/swift/blob/master/docs/StringManifesto.md#comparing-and-hashing-strings> >> [5] Unifying Linux/Darwin ASCII sort order semantics - github >> <https://github.com/milseman/swift/commit/5560e13198d5cc284f46bf190f59a2edf7ed747b>_______________________________________________ >> swift-dev mailing list >> swift-dev@swift.org <mailto:swift-dev@swift.org> >> https://lists.swift.org/mailman/listinfo/swift-dev >> <https://lists.swift.org/mailman/listinfo/swift-dev> > > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org <mailto:swift-dev@swift.org> > https://lists.swift.org/mailman/listinfo/swift-dev > <https://lists.swift.org/mailman/listinfo/swift-dev> > > > _______________________________________________ > swift-dev mailing list > swift-dev@swift.org > https://lists.swift.org/mailman/listinfo/swift-dev
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