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MINOR: time: avoid unneeded updates to now_offset

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The time adjustment is very rare, even at high pool rates. Tests show
that only 0.2% of tv_update_date() calls require a change of offset. Such
concurrent writes to a shared variable have an important impact on future
loads, so let's only update the variable if it changed.
This commit is contained in:
Willy Tarreau 2021-04-23 15:17:27 +02:00
parent a6f9c5d2a7
commit 481795de13
1 changed files with 6 additions and 3 deletions
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9
src/time.c
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@ -184,7 +184,7 @@ void tv_update_date(int max_wait, int interrupted)
unsigned int old_now_ms;
unsigned long long old_now;
unsigned long long new_now;
ullong ofs = HA_ATOMIC_LOAD(&now_offset);
ullong ofs, ofs_new;
uint sec_ofs, usec_ofs;
gettimeofday(&date, NULL);
@ -203,6 +203,8 @@ void tv_update_date(int max_wait, int interrupted)
_tv_ms_add(&min_deadline, &before_poll, max_wait);
_tv_ms_add(&max_deadline, &before_poll, max_wait + 100);
ofs = HA_ATOMIC_LOAD(&now_offset);
if (unlikely(__tv_islt(&date, &before_poll) || // big jump backwards
(!interrupted && __tv_islt(&date, &min_deadline)) || // small jump backwards
__tv_islt(&max_deadline, &date))) { // big jump forwards
@ -265,8 +267,9 @@ void tv_update_date(int max_wait, int interrupted)
usec_ofs += 1000000;
sec_ofs -= 1;
}
ofs = ((ullong)sec_ofs << 32) + usec_ofs;
HA_ATOMIC_STORE(&now_offset, ofs);
ofs_new = ((ullong)sec_ofs << 32) + usec_ofs;
if (ofs_new != ofs)
HA_ATOMIC_STORE(&now_offset, ofs_new);
}
/* must be called once at boot to initialize some global variables */