From 58f5f45566b827e74ff623398bdf6d0b6fcebdb3 Mon Sep 17 00:00:00 2001 From: Rickard Green Date: Fri, 18 Nov 2011 12:46:43 +0100 Subject: Use unbound schedulers as default As of ERTS version 5.9 (OTP-R15B) the runtime system will by default not bind schedulers to logical processors. If the Erlang runtime system is the only operating system process that binds threads to logical processors, this improves the performance of the runtime system. However, if other operating system processes (as for example another Erlang runtime system) also bind threads to logical processors, there might be a performance penalty instead. In some cases this performance penalty might be severe. Due to this, we change the default so that the user must make an active decision in order to bind schedulers. --- erts/doc/src/erl.xml | 50 +++++++++++------------------------ erts/doc/src/erlang.xml | 14 ++++------ erts/emulator/beam/erl_cpu_topology.c | 12 ++------- 3 files changed, 23 insertions(+), 53 deletions(-) diff --git a/erts/doc/src/erl.xml b/erts/doc/src/erl.xml index 02082e57c6..048ffbcd47 100644 --- a/erts/doc/src/erl.xml +++ b/erts/doc/src/erl.xml @@ -41,25 +41,11 @@ to scroll back to text which has scrolled off the screen. The program must be used, however, in pipelines or if you want to redirect standard input or output.

-

As of ERTS version 5.8 (OTP-R14A) the runtime system will by - default bind schedulers to logical processors using the - default_bind bind type if the amount of schedulers are - at least equal to the amount of logical processors configured, - binding of schedulers is supported, and a CPU topology is - available at startup. -

- If the Erlang runtime system is the only operating system - process that binds threads to logical processors, this - improves the performance of the runtime system. However, - if other operating system processes (as for example - another Erlang runtime system) also bind threads to - logical processors, there might be a performance penalty - instead. If this is the case you, are are advised to - unbind the schedulers using the - +sbtu command line argument, - or by invoking - erlang:system_flag(scheduler_bind_type, - unbound).

+

As of ERTS version 5.9 (OTP-R15B) the runtime system will by + default not bind schedulers to logical processors. + For more information see documentation of the + +sbt system flag. +

@@ -718,22 +704,18 @@ that the +sct flag may have to be passed before the +sbt flag on the command line (in case no CPU topology has been automatically detected).

-

The runtime system will by default bind schedulers to logical - processors using the default_bind bind type if the amount - of schedulers are at least equal to the amount of logical - processors configured, binding of schedulers is supported, - and a CPU topology is available at startup. +

The runtime system will by default not bind schedulers + to logical processors.

-

NOTE: If the Erlang runtime system is the only operating - system process that binds threads to logical processors, this - improves the performance of the runtime system. However, if other - operating system processes (as for example another Erlang runtime - system) also bind threads to logical processors, there might be a - performance penalty instead. If this is the case you, are advised - to unbind the schedulers using the +sbtu command line - argument, or by invoking - erlang:system_flag(scheduler_bind_type, - unbound).

+

NOTE: If the Erlang runtime system is the only operating system + process that binds threads to logical processors, this + improves the performance of the runtime system. However, + if other operating system processes (as for example + another Erlang runtime system) also bind threads to + logical processors, there might be a performance penalty + instead. In some cases this performance penalty might be + severe. If this is the case, you are advised to not + bind the schedulers.

For more information, see erlang:system_flag(scheduler_bind_type, SchedulerBindType).

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml index aef31f5b98..ae6300a728 100644 --- a/erts/doc/src/erlang.xml +++ b/erts/doc/src/erlang.xml @@ -5173,21 +5173,17 @@ true For more information on how to define the CPU topology, see erlang:system_flag(cpu_topology, CpuTopology).

-

The runtime system will by default bind schedulers to logical - processors using the default_bind bind type if the amount - of schedulers are at least equal to the amount of logical - processors configured, binding of schedulers is supported, - and a CPU topology is available at startup. +

The runtime system will by default not bind schedulers + to logical processors.

NOTE: If the Erlang runtime system is the only operating system process that binds threads to logical processors, this improves the performance of the runtime system. However, if other operating system processes (as for example another Erlang runtime system) also bind threads to logical processors, there - might be a performance penalty instead. If this is the case you, - are are advised to unbind the schedulers using the - +sbtu command line argument, - or erlang:system_flag(scheduler_bind_type, unbound).

+ might be a performance penalty instead. In some cases this + performance penalty might be severe. If this is the case, you + are advised to not bind the schedulers.

Schedulers can be bound in different ways. The How argument determines how schedulers are bound. How can currently be one of:

diff --git a/erts/emulator/beam/erl_cpu_topology.c b/erts/emulator/beam/erl_cpu_topology.c index 03c0ef904a..cc930ba1e3 100644 --- a/erts/emulator/beam/erl_cpu_topology.c +++ b/erts/emulator/beam/erl_cpu_topology.c @@ -1729,16 +1729,8 @@ erts_init_cpu_topology(void) scheduler2cpu_map[ix].bound_id = -1; } - if (cpu_bind_order == ERTS_CPU_BIND_UNDEFINED) { - int ncpus = erts_get_cpu_configured(cpuinfo); - if (ncpus < 1 || erts_no_schedulers < ncpus) - cpu_bind_order = ERTS_CPU_BIND_NONE; - else - cpu_bind_order = ((system_cpudata || user_cpudata) - && (erts_bind_to_cpu(cpuinfo, -1) != -ENOTSUP) - ? ERTS_CPU_BIND_DEFAULT_BIND - : ERTS_CPU_BIND_NONE); - } + if (cpu_bind_order == ERTS_CPU_BIND_UNDEFINED) + cpu_bind_order = ERTS_CPU_BIND_NONE; reader_groups_map = add_cpu_groups(reader_groups, reader_groups_callback, -- cgit v1.2.3