From a4f18f133b2b9032d41246c27f1186a5b9b55346 Mon Sep 17 00:00:00 2001 From: Henning Baldersheim Date: Mon, 20 Apr 2020 18:03:23 +0000 Subject: There are so many combinations that the libstdc++ library can be built that the performance you get from std::chrono::system_clock and stxad::chrono::steady_clock has a dramatic performance difference. On RHEL7/Centos with an witout this patch is 18ns vs 550ns. --- vespalib/src/vespa/vespalib/util/time.cpp | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+) (limited to 'vespalib') diff --git a/vespalib/src/vespa/vespalib/util/time.cpp b/vespalib/src/vespa/vespalib/util/time.cpp index 46cf4806dfc..2e8f4e7e30e 100644 --- a/vespalib/src/vespa/vespalib/util/time.cpp +++ b/vespalib/src/vespa/vespalib/util/time.cpp @@ -52,3 +52,29 @@ Timer::waitAtLeast(duration dur, bool busyWait) { } } + +namespace std::chrono { + +// This is a hack to avoid the slow clock computations on RHEL7/CentOS 7 due to using systemcalls. +// This brings cost down from 550-560ns to 18-19ns + +inline namespace _V2 { + +system_clock::time_point +system_clock::now() noexcept { + timespec tp; + clock_gettime(CLOCK_REALTIME, &tp); + return time_point(duration(chrono::seconds(tp.tv_sec) + + chrono::nanoseconds(tp.tv_nsec))); +} + +steady_clock::time_point +steady_clock::now() noexcept { + timespec tp; + clock_gettime(CLOCK_MONOTONIC, &tp); + return time_point(duration(chrono::seconds(tp.tv_sec) + + chrono::nanoseconds(tp.tv_nsec))); +} + +} +} -- cgit v1.2.3