2af04860f6
Constantly re-reading the timezone information only to be told the exact same thing is wildly expensive, which can hurt in operations that cause a lot of QTimeZone creation, for example, V4's DateObject - which creates them a lot (in DaylightSavingTA). This performance problem was identified when I noticed that a QDateTime binding updated once per frame was causing >100% CPU usage (on a desktop!) thanks to a QtQuickControls 1 Calendar (which has a number of bindings to the date's properties like getMonth() and so on). The newly added tst_QTimeZone::systemTimeZone benchmark gets a ~90% decrease in instruction count: --- before +++ after PASS : tst_QTimeZone::systemTimeZone() RESULT : tst_QTimeZone::systemTimeZone(): - 0.024 msecs per iteration (total: 51, iterations: 2048) + 0.0036 msecs per iteration (total: 59, iterations: 16384) Also impacted (over in QDateTime) is tst_QDateTime::setMSecsSinceEpochTz(). The results here are - on the surface - less impressive (~0.17% drop), however, it isn't even creating QTimeZone on a hot path to begin with, so a large drop would have been a surprise. Added several further benchmarks to cover non-system zones and traverse transitions. Done-With: Edward Welbourne <edward.welbourne@qt.io> Task-number: QTBUG-75585 Change-Id: I044a84fc2d3a2dc965f63cd3a3299fc509750bf7 Reviewed-by: Ulf Hermann <ulf.hermann@qt.io> Reviewed-by: Simon Hausmann <simon.hausmann@qt.io> |
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| codecs | ||
| io | ||
| json | ||
| kernel | ||
| mimetypes | ||
| plugin | ||
| text | ||
| thread | ||
| time | ||
| tools | ||
| corelib.pro | ||