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File 5771-erts-Use-multi-time-warp-mode-by-default.patch of Package erlang
From c0f293afcecca2007805ecd02fe9017052425428 Mon Sep 17 00:00:00 2001 From: Rickard Green <rickard@erlang.org> Date: Fri, 3 Jun 2022 14:10:38 +0200 Subject: [PATCH] [erts] Use multi time warp mode by default --- erts/doc/src/time_correction.xml | 60 +++++++++++-------- erts/emulator/beam/erl_init.c | 2 +- .../upcoming_incompatibilities.xml | 13 ---- 3 files changed, 36 insertions(+), 39 deletions(-) diff --git a/erts/doc/src/time_correction.xml b/erts/doc/src/time_correction.xml index b3a36b907e..17263c26fe 100644 --- a/erts/doc/src/time_correction.xml +++ b/erts/doc/src/time_correction.xml @@ -34,29 +34,42 @@ </header> <section> - <title>New Extended Time Functionality</title> - <note><p>As from Erlang/OTP 18 (ERTS 7.0) the time functionality - has been extended. This includes a + <title>Extended Time Functionality</title> + + <p>As of Erlang/OTP 18 (ERTS 7.0) the time functionality + was extended. This includes a <seeguide marker="#The_New_Time_API">new API</seeguide> for time and <seeguide marker="#Time_Warp_Modes">time warp modes</seeguide> that change the system behavior when system time changes.</p> - <p>The <seeguide marker="#No_Time_Warp_Mode">default - time warp mode</seeguide> has the same behavior as before, and the - old API still works. Thus, you are not required to change - anything unless you want to. However, <em>you are strongly - encouraged to use the new API</em> instead of the old API based - on <seemfa marker="erlang#now/0"><c>erlang:now/0</c></seemfa>. - <c>erlang:now/0</c> is deprecated, as it is and - will be a scalability bottleneck.</p> - - <p>By using the new API, you - automatically get scalability and performance improvements. This - also enables you to use the - <seeguide marker="#Multi_Time_Warp_Mode">multi-time warp mode</seeguide> - that improves accuracy and precision of time measurements.</p> + <note> + <p> + As of Erlang/OTP 26 (ERTS 14.0) the + <seeguide marker="#Multi_Time_Warp_Mode">multi time warp + mode</seeguide> is enabled by default. This assumes that all + code executing on the system is + <seeguide marker="#Time_Warp_Safe_Code">time warp safe</seeguide>. + </p> + <p> + If you have old code in the system that is not time warp + safe, you now explicitly need to start the system in + <seeguide marker="#No_Time_Warp_Mode">no time warp + mode</seeguide> (or + <seeguide marker="#Single_Time_Warp_Mode">singe time warp + mode</seeguide> if it is partially time warp safe) in order + to avoid problems. When starting the system in no time warp + mode, the system behaves as it did prior to the introduction + of the extended time functionality introduced in OTP 18. + </p> + <p> + If you have code that is not time warp safe, you are strongly + encouraged to change this so that you can use multi time + warp mode. Compared to no time warp mode, multi time warp + mode improves scalability and performance as well as accuracy + and precision of time measurements. + </p> </note> </section> @@ -405,13 +418,9 @@ <section> <title>No Time Warp Mode</title> <p>The time offset is determined at runtime system start - and does not change later. This is the default behavior, but - not because it is the best mode (which it is not). It is - default <em>only</em> because this is how the runtime system - behaved until ERTS 7.0. - Ensure that your Erlang code that can execute during a time - warp is <seeguide marker="#Time_Warp_Safe_Code">time warp - safe</seeguide> before enabling other modes.</p> + and does not change later. This is the same behavior as was + default prior to OTP 26 (ERTS 14.0), and the only behavior + prior to OTP 18 (ERTS 7.0).</p> <p>As the time offset is not allowed to change, time correction must adjust the frequency of the Erlang @@ -558,7 +567,8 @@ better, and behave better on almost all platforms. Also, the accuracy and precision of time measurements are better. Only Erlang runtime systems executing on - ancient platforms benefit from another configuration.</p> + ancient platforms benefit from another configuration. + As of OTP 26 (ERTS 14.0) this is also the default.</p> <p>The time offset can change at any time without limitations. That is, Erlang system time can perform time warps both diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c index 872fa6b613..62c11668ed 100644 --- a/erts/emulator/beam/erl_init.c +++ b/erts/emulator/beam/erl_init.c @@ -275,7 +275,7 @@ static ERTS_INLINE void set_default_time_adj(int *time_correction_p, ErtsTimeWarpMode *time_warp_mode_p) { *time_correction_p = 1; - *time_warp_mode_p = ERTS_NO_TIME_WARP_MODE; + *time_warp_mode_p = ERTS_MULTI_TIME_WARP_MODE; if (!erts_check_time_adj_support(*time_correction_p, *time_warp_mode_p)) { *time_correction_p = 0; diff --git a/system/doc/general_info/upcoming_incompatibilities.xml b/system/doc/general_info/upcoming_incompatibilities.xml index 59003d2243..90774672bd 100644 --- a/system/doc/general_info/upcoming_incompatibilities.xml +++ b/system/doc/general_info/upcoming_incompatibilities.xml @@ -132,18 +132,5 @@ </p> </section> - <section> - <title>The default timewarp mode will change to multi-time warp mode</title> - <p> - The default <seeguide marker="erts:time_correction#Time_Warp_Modes"> - Time Warp Mode</seeguide> will be changed from - <seeguide marker="erts:time_correction#No_Time_Warp_Mode"> - no time warp mode</seeguide> to <seeguide marker="erts:time_correction#Multi_Time_Warp_Mode"> - multi-time warp mode</seeguide>. See <seeguide marker="erts:time_correction"> - Time and Time Correction in Erlang</seeguide> for details on how this will - effect your system. - </p> - </section> - </section> </chapter> -- 2.35.3
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