bthread: support per-tag CPU affinity in --cpu_set by yanglimingcn · Pull Request #3331 · apache/brpc

yanglimingcn · 2026-06-05T06:13:57Z

Previously --cpu_set accepted a single CPU list (e.g. "0-3,5,7") that was applied uniformly to all bthread worker threads regardless of their bthread_tag.

This change extends the flag to accept a per-tag format:

--cpu_set="0:0-3,5,7;1:6-9,4"

where each semicolon-separated segment is ":". Tags not mentioned in the string get no CPU binding. The legacy single-list format continues to work unchanged and binds all tags to the same set.

Implementation:

Replace _cpus (vector) with _tag_cpus (vector<vector>), sized to FLAGS_task_group_ntags in the constructor.
Add parse_one_cpuset() (static helper) for the existing range-list parsing logic; parse_cpuset() now dispatches between legacy and per-tag formats based on the presence of ':' or ';'.
worker_thread() looks up _tag_cpus[tag] and round-robins over the per-tag CPU list using the global _next_worker_id counter.

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

What is changed and the side effects?

Changed:

Side effects:

Performance effects:
Breaking backward compatibility:

Check List:

Please make sure your changes are compilable.
When providing us with a new feature, it is best to add related tests.
Please follow Contributor Covenant Code of Conduct.

Copilot

Pull request overview

This PR extends the --cpu_set flag in bthread::TaskControl to support per-bthread_tag CPU affinity (while preserving the legacy single CPU-list format), enabling different worker-thread tags to be pinned to different CPU sets.

Changes:

Update --cpu_set flag documentation and parsing to accept tag:cpu-list segments separated by ;.
Replace the single shared CPU list with a per-tag CPU list (_tag_cpus).
Apply CPU binding per worker based on its tag’s CPU list.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/bthread/task_control.h	Updates `parse_cpuset` API/doc and adds `_tag_cpus` per-tag CPU binding storage.
src/bthread/task_control.cpp	Implements per-tag `cpu_set` parsing and applies per-tag affinity during worker thread startup.

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+    // worker_id is global and monotonically increasing; it doubles as the
+    // round-robin index for CPU affinity (same counter for name and binding).
+    int worker_id = c->_next_worker_id.fetch_add(1, butil::memory_order_relaxed);
+    if (!c->_tag_cpus[tag].empty()) {
+        const auto& cpus = c->_tag_cpus[tag];
+        bind_thread_to_cpu(pthread_self(), cpus[worker_id % cpus.size()]);


+int TaskControl::parse_cpuset(const std::string& value,
+                              std::vector<std::vector<unsigned>>& tag_cpus,
+                              int ntags) {
+    if (value.empty()) {
+        return -1;
+    }
+    // Detect per-tag format by the presence of ':' or ';'.
+    // Legacy format ("0-3,5,7") never contains these characters.
+    bool per_tag_format = (value.find(';') != std::string::npos ||
+                           value.find(':') != std::string::npos);
+


+            std::string tag_str  = segment.substr(0, colon);
+            std::string cpus_str = segment.substr(colon + 1);
+
+            unsigned tag_id = 0;
+            butil::StringPiece tag_sp(tag_str);
+            if (butil::StringSplitter(tag_sp, '\t').to_uint(&tag_id) != 0) {
+                LOG(ERROR) << "cpu_set invalid tag '" << tag_str << "'";
+                return -1;


+    // On success populates |tag_cpus| (indexed by tag) and returns 0.
+    // |tag_cpus| is resized to max_tag+1; tags that are not mentioned
+    // get an empty cpu list (= no binding).
+    // Returns -1 on parse error.
+    static int parse_cpuset(const std::string& value,
+                            std::vector<std::vector<unsigned>>& tag_cpus,
+                            int ntags);


+int TaskControl::parse_cpuset(const std::string& value,
+                              std::vector<std::vector<unsigned>>& tag_cpus,
+                              int ntags) {
+    if (value.empty()) {
+        return -1;
+    }
+    // Detect per-tag format by the presence of ':' or ';'.
+    // Legacy format ("0-3,5,7") never contains these characters.
+    bool per_tag_format = (value.find(';') != std::string::npos ||
+                           value.find(':') != std::string::npos);
+


Previously --cpu_set accepted a single CPU list (e.g. "0-3,5,7") that was applied uniformly to all bthread worker threads regardless of their bthread_tag. This change extends the flag to accept a per-tag format: --cpu_set="0:0-3,5,7;1:6-9,4" where each semicolon-separated segment is "<tag>:<cpu-list>". Tags not mentioned in the string get no CPU binding. The legacy single-list format continues to work unchanged and binds all tags to the same set. Implementation: - Replace _cpus (vector<unsigned>) with _tag_cpus (vector<vector<unsigned>>), sized to FLAGS_task_group_ntags in the constructor. - Add parse_one_cpuset() (static helper) for the existing range-list parsing logic; parse_cpuset() now dispatches between legacy and per-tag formats based on the presence of ':' or ';'. - worker_thread() looks up _tag_cpus[tag] and round-robins over the per-tag CPU list using the global _next_worker_id counter.

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 3 comments.

    , _tagged_pl(FLAGS_task_group_ntags)
+    , _tag_cpus(FLAGS_task_group_ntags)
+    , _tag_next_worker_id(FLAGS_task_group_ntags)
 {}


+        for (auto i = first; i <= last; ++i) {
+            cpuset.insert(i);
+        }


+    // tag_wid is a per-tag monotonic counter: same-tag workers get 0,1,2,...
+    // Used both for CPU round-robin affinity and the thread name suffix.
+    int tag_wid = c->_tag_next_worker_id[tag].fetch_add(
+                      1, butil::memory_order_relaxed);


chenBright

LGTM

yanglimingcn requested a review from Copilot June 5, 2026 06:14

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yanglimingcn force-pushed the feature/cpu_set_support_multi_tag branch from e29075d to 6538752 Compare June 5, 2026 06:20

yanglimingcn force-pushed the feature/cpu_set_support_multi_tag branch from 6538752 to 41e3f24 Compare June 5, 2026 07:00

yanglimingcn requested a review from Copilot June 5, 2026 07:11

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chenBright reviewed Jun 6, 2026

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bthread: support per-tag CPU affinity in --cpu_set#3331

bthread: support per-tag CPU affinity in --cpu_set#3331
yanglimingcn wants to merge 1 commit into
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yanglimingcn:feature/cpu_set_support_multi_tag

yanglimingcn commented Jun 5, 2026

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yanglimingcn commented Jun 5, 2026

What problem does this PR solve?

What is changed and the side effects?

Check List:

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