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authorLukas Larsson <[email protected]>2015-07-16 15:36:44 +0200
committerLukas Larsson <[email protected]>2016-02-02 10:45:22 +0100
commit6090f9c7e9b0ddbccef357641c1455475b348e94 (patch)
tree05651df115da49195739fa11009bc9c225f85ce8 /erts/emulator/sys/unix/sys_time.c
parent0399f5fc547ef035c4eb5e383f30b28ae73d936e (diff)
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erts: Add power saving cpu feature tests and use them
Diffstat (limited to 'erts/emulator/sys/unix/sys_time.c')
-rw-r--r--erts/emulator/sys/unix/sys_time.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/erts/emulator/sys/unix/sys_time.c b/erts/emulator/sys/unix/sys_time.c
index 9738a8c352..03d39c7ce6 100644
--- a/erts/emulator/sys/unix/sys_time.c
+++ b/erts/emulator/sys/unix/sys_time.c
@@ -971,18 +971,18 @@ static ErtsSysPerfCounter calculate_perf_counter_unit(void) {
static int have_rdtscp(void)
{
#if defined(ETHR_X86_RUNTIME_CONF__)
- /* On early x86 cpu's the tsc varies with
- the current speed of the cpu, which means that the time per
- tick vary depending on the current load of the cpu. We do not
- want this as it would give very scewed numbers when the cpu is
- mostly idle.
- If we have the rdtscp feature it is a sign that the cpu is
- relatively modern, and thus the tsc quite stable so we use it then.
+ /* On early x86 cpu's the tsc varies with the current speed of the cpu,
+ which means that the time per tick vary depending on the current
+ load of the cpu. We do not want this as it would give very scewed
+ numbers when the cpu is mostly idle.
+ The linux kernel seems to think that checking for constant and
+ reliable is enough to trust the counter so we do the same.
If this test is not good enough, I don't know what we'll do.
Maybe fallback on erts_sys_hrtime always, but that would be a shame as
rdtsc is about 3 times faster than hrtime... */
- return ETHR_X86_RUNTIME_CONF_HAVE_RDTSCP__;
+ return ETHR_X86_RUNTIME_CONF_HAVE_CONSTANT_TSC__ &&
+ ETHR_X86_RUNTIME_CONF_HAVE_TSC_RELIABLE__;
#else
return 0;
#endif