From eea5f896780e07f7ca76685061d01e7be5a7abaa Mon Sep 17 00:00:00 2001 From: Lukas Larsson Date: Thu, 11 Sep 2014 18:26:26 +0200 Subject: erts, kernel: Add os:perf_counter function The perf_counter is a very very cheap and high resolution timer that can be used to timestamp system events. It does not have monoticity guarantees, but should on most OS's expose a monotonous time. A special instruction has been created for this counter to further speed up fetching it. OTP-12908 --- lib/kernel/doc/src/os.xml | 25 ++++++++++++++++++++++++ lib/kernel/src/os.erl | 16 ++++++++++++++- lib/kernel/test/os_SUITE.erl | 46 +++++++++++++++++++++++++++++++++++++++++--- 3 files changed, 83 insertions(+), 4 deletions(-) (limited to 'lib/kernel') diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml index 682d4a2eac..165160a909 100644 --- a/lib/kernel/doc/src/os.xml +++ b/lib/kernel/doc/src/os.xml @@ -37,6 +37,7 @@ use these functions can be of help in enabling a program to run on most platforms.

+ @@ -209,6 +210,30 @@ format_utc_timestamp() -> and os:system_time/1.

 + + + Returns a performance counter + +

Returns the current performance counter value in perf_counter + time unit. + This is a highly optimized call that might not be traceable. +

+ + + + + Returns a performance counter +

Returns a performance counter that can be used as a very fast and + high resolution timestamp. This counter is read directly from the hardware or operating + system with the same guarantees. This means that two consecutive calls + to the function are not guaranteed to be monotonic, though it most likely will be. + The performance counter till be converted to the resolution passed as an argument.

+ 
1> T1 = os:perf_counter(1000),receive after 10000 -> ok end,T2 = os:perf_counter(1000).
+176525861
+2> T2 - T1.
+10004
+ + Return the OS family and, in some cases, OS name of the current operating system diff --git a/lib/kernel/src/os.erl b/lib/kernel/src/os.erl index 0022959c11..4947088635 100644 --- a/lib/kernel/src/os.erl +++ b/lib/kernel/src/os.erl @@ -27,7 +27,9 @@ %%% BIFs --export([getenv/0, getenv/1, getenv/2, getpid/0, putenv/2, system_time/0, system_time/1, +-export([getenv/0, getenv/1, getenv/2, getpid/0, + perf_counter/0, perf_counter/1, + putenv/2, system_time/0, system_time/1, timestamp/0, unsetenv/1]). -spec getenv() -> [string()]. @@ -60,6 +62,18 @@ getenv(VarName, DefaultValue) -> getpid() -> erlang:nif_error(undef). +-spec perf_counter() -> Counter when + Counter :: integer(). + +perf_counter() -> + erlang:nif_error(undef). + +-spec perf_counter(Unit) -> integer() when + Unit :: erlang:time_unit(). + +perf_counter(Unit) -> + erlang:convert_time_unit(os:perf_counter(), perf_counter, Unit). + -spec putenv(VarName, Value) -> true when VarName :: string(), Value :: string(). diff --git a/lib/kernel/test/os_SUITE.erl b/lib/kernel/test/os_SUITE.erl index 83a95019e7..e6e8568394 100644 --- a/lib/kernel/test/os_SUITE.erl +++ b/lib/kernel/test/os_SUITE.erl @@ -20,10 +20,11 @@ -module(os_SUITE). -export([all/0, suite/0,groups/0,init_per_suite/1, end_per_suite/1, - init_per_group/2,end_per_group/2]). + init_per_group/2,end_per_group/2, + init_per_testcase/2,end_per_testcase/2]). -export([space_in_cwd/1, quoting/1, cmd_unicode/1, space_in_name/1, bad_command/1, find_executable/1, unix_comment_in_command/1, deep_list_command/1, - large_output_command/1]). + large_output_command/1, perf_counter_api/1]). -include_lib("test_server/include/test_server.hrl"). @@ -32,7 +33,7 @@ suite() -> [{ct_hooks,[ts_install_cth]}]. all() -> [space_in_cwd, quoting, cmd_unicode, space_in_name, bad_command, find_executable, unix_comment_in_command, deep_list_command, - large_output_command]. + large_output_command, perf_counter_api]. groups() -> []. @@ -49,6 +50,11 @@ init_per_group(_GroupName, Config) -> end_per_group(_GroupName, Config) -> Config. +init_per_testcase(_TC,Config) -> + Config. + +end_per_testcase(_,_Config) -> + ok. space_in_cwd(doc) -> "Test that executing a command in a current working directory " @@ -278,6 +284,40 @@ large_output_command(Config) when is_list(Config) -> AAA = lists:duplicate(7000, $a), comp(AAA,os:cmd("echo " ++ AAA)). +%% Test that the os:perf_counter api works as expected +perf_counter_api(_Config) -> + + true = is_integer(os:perf_counter()), + true = os:perf_counter() > 0, + + T1 = os:perf_counter(), + timer:sleep(100), + T2 = os:perf_counter(), + TsDiff = erlang:convert_time_unit(T2 - T1, perf_counter, nano_seconds), + ct:pal("T1: ~p~n" + "T2: ~p~n" + "TsDiff: ~p~n", + [T1,T2,TsDiff]), + + %% We allow a 15% diff + true = TsDiff < 115000000, + true = TsDiff > 85000000, + + T1Ms = os:perf_counter(1000), + timer:sleep(100), + T2Ms = os:perf_counter(1000), + MsDiff = T2Ms - T1Ms, + ct:pal("T1Ms: ~p~n" + "T2Ms: ~p~n" + "MsDiff: ~p~n", + [T1Ms,T2Ms,MsDiff]), + + %% We allow a 15% diff + true = MsDiff < 115, + true = MsDiff > 85. + +%% Util functions + comp(Expected, Got) -> case strip_nl(Got) of Expected -> -- cgit v1.2.3