chenBright commented on code in PR #3009:
URL: https://github.com/apache/brpc/pull/3009#discussion_r2173632622
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src/bthread/task_control.cpp:
##########
@@ -524,12 +525,29 @@ void TaskControl::print_rq_sizes(std::ostream& os) {
double TaskControl::get_cumulated_worker_time() {
int64_t cputime_ns = 0;
+ int64_t now = butil::cpuwide_time_ns();
BAIDU_SCOPED_LOCK(_modify_group_mutex);
for_each_task_group([&](TaskGroup* g) {
if (g) {
- cputime_ns += g->_cumulated_cputime_ns;
+ // With the acquire-release atomic operation, the CPU time of the
bthread is
+ // only calculated once through `_cumulated_cputime_ns' or
`_last_run_ns'.
+ cputime_ns +=
g->_cumulated_cputime_ns.load(butil::memory_order_acquire);
+ // The bthread is still running on the worker,
+ // so we need to add the elapsed time since it started.
+ // In extreme cases, before getting `_last_run_ns_in_tc',
+ // `_last_run_ns_in_tc' may have been updated multiple times,
+ // and `cputime_ns' will miss some cpu time, which is ok.
+ int64_t last_run_ns = g->_last_run_ns;
+ if (last_run_ns > _last_get_cumulated_time_ns) {
+ g->_last_run_ns_in_tc = last_run_ns;
+ cputime_ns += now - last_run_ns;
+ } else if (last_run_ns == g->_last_run_ns_in_tc) {
+ // The bthread is still running on the same worker.
+ cputime_ns += now - last_run_ns;
+ }
Review Comment:
https://rigtorp.se/isatomic/
> On the latest CPU microarchitectures (Skylake and Zen 2) AVX/AVX2
128b/256b aligned loads and stores are atomic even though Intel and AMD
officially doesn’t guarantee this.
Perhaps we can use the implicit feature of modern CPUs that 128-bit aligned
load/store operations are atomic to implement atomic operations on combination
of `_cumulated_cputime_ns` and `_last_run_ns`.
x86_64: `_mm_load_si128`, `_mm_store_si128`
Arm and later: `vld1q_s64`
For scenarios that do not support 128-bit atomic operations, use the lock to
guarantee this. Only the worker thread and sample thread acquire the lock, and
the sample thread acquires locks once a second. There is no lock contention
between worker threads. So lock contention can be ignored.
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