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throttle: add delays to match deferred request rate to btrfs completion rate

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Measure the time spent running various operations that extend btrfs
transaction completion times (`LOGICAL_INO`, tmpfiles, and dedupe)
and arrange for each operation to run for not less than the average
amount of time by adding a sleep after each operation that takes less
than the average.

The delay after each operation is intended to slow down the rate of
deferred and long-running requests from bees to match the rate at which
btrfs is actually completing them.  This may help avoid big spikes in
latency if btrfs has so many requests queued that it has to force a
commit to release memory.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell
2024-12-10 00:36:28 -05:00
parent f209cafcd8
commit ea45982293
4 changed files with 58 additions and 9 deletions
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46
src/bees.cc
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@@ -305,6 +305,48 @@ bees_unreadahead(int const fd, off_t offset, size_t size)
BEESCOUNTADD(readahead_unread_ms, unreadahead_timer.age() * 1000);
}
static double bees_throttle_factor = 1.0;
void
bees_throttle(const double time_used, const char *const context)
{
static mutex s_mutex;
unique_lock<mutex> throttle_lock(s_mutex);
struct time_pair {
double time_used = 0;
double time_count = 0;
double longest_sleep_time = 0;
};
static map<string, time_pair> s_time_map;
auto &this_time = s_time_map[context];
auto &this_time_used = this_time.time_used;
auto &this_time_count = this_time.time_count;
auto &longest_sleep_time = this_time.longest_sleep_time;
this_time_used += time_used;
++this_time_count;
// Keep the timing data fresh
static Timer s_fresh_timer;
if (s_fresh_timer.age() > 300) {
s_fresh_timer.reset();
this_time_count *= 0.9;
this_time_used *= 0.9;
}
// Wait for enough data to calculate rates
if (this_time_used < 1.0 || this_time_count < 1.0) return;
const auto avg_time = this_time_used / this_time_count;
const auto sleep_time = min(60.0, bees_throttle_factor * avg_time - time_used);
if (sleep_time <= 0) {
return;
}
if (sleep_time > longest_sleep_time) {
BEESLOGDEBUG(context << ": throttle delay " << sleep_time << " s, time used " << time_used << " s, avg time " << avg_time << " s");
longest_sleep_time = sleep_time;
}
throttle_lock.unlock();
BEESNOTE(context << ": throttle delay " << sleep_time << " s, time used " << time_used << " s, avg time " << avg_time << " s");
nanosleep(sleep_time);
}
thread_local random_device bees_random_device;
thread_local uniform_int_distribution<default_random_engine::result_type> bees_random_seed_dist(
numeric_limits<default_random_engine::result_type>::min(),
@@ -401,6 +443,8 @@ BeesTempFile::resize(off_t offset)
// Count time spent here
BEESCOUNTADD(tmp_resize_ms, resize_timer.age() * 1000);
bees_throttle(resize_timer.age(), "tmpfile_resize");
}
void
@@ -536,6 +580,8 @@ BeesTempFile::make_copy(const BeesFileRange &src)
}
BEESCOUNTADD(tmp_copy_ms, copy_timer.age() * 1000);
bees_throttle(copy_timer.age(), "tmpfile_copy");
BEESCOUNT(tmp_copy);
return rv;
}