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[TENT] SelectionPolicy: per-policy SL/TC/qp_pool schema (RFC #2568 step 1) #2640

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[TENT] SelectionPolicy: per-policy SL/TC/qp_pool schema (RFC #2568 step 1) #2640

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19 changes: 19 additions & 0 deletions mooncake-transfer-engine/tent/include/tent/runtime/transport_selector.h
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Original file line number Diff line number Diff line change
Expand Up @@ -117,6 +117,19 @@ struct SelectionPolicy {

// Transport preference list (evaluated in order)
std::vector<TransportType> transports;

// --- Link-layer QoS attributes (RFC #2519 / #2568, step-1 schema only) ---

@staryxchen staryxchen Jun 26, 2026

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I think add the comments about the RFC reference and splited step is not necessary

// These let a policy carry per-policy fabric QoS instead of the
// process-global MC_IB_SL / MC_IB_TC. nullopt = fall back to the global
// RdmaParams value (today's behavior). InfiniBand Service Level (0-15) and
// Traffic Class / DSCP (0-255).
std::optional<int> service_level; // nullopt = use global default
std::optional<int> traffic_class; // nullopt = use global default
// Named QP pool this policy's traffic should land on. Reserved here so the
// schema is forward-compatible: step 1 only parses/stores it; the actual
// per-class QP pool creation and routing is a follow-up (step 2). Unset =
// the current single "data QP" path.
std::optional<std::string> qp_pool;
};

/**
Expand All @@ -125,6 +138,12 @@ struct SelectionPolicy {
struct SelectionResult {
TransportType transport = UNSPEC;
uint64_t device_mask = ~0ULL; // Bitmask of allowed devices (~0 = all)
// Resolved link-layer QoS from the matched policy (RFC #2519 / #2568).
// nullopt = use the global RdmaParams default. Carried here for the
// follow-up that applies them at QP setup; step 1 only plumbs the values.
std::optional<int> service_level;
std::optional<int> traffic_class;
std::optional<std::string> qp_pool;
};

/**
Expand Down
35 changes: 35 additions & 0 deletions mooncake-transfer-engine/tent/src/runtime/transport_selector.cpp
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Expand Up @@ -206,6 +206,34 @@ void TransportSelector::loadPolicies() {
}
}

// Parse link-layer QoS attributes (RFC #2519 / #2568, step 1: stored
// only, not yet applied to QPs). Out-of-range values are ignored so a
// bad config never breaks selection.
if (policy_json.contains("service_level")) {
int sl = policy_json.value("service_level", -1);
if (sl >= 0 && sl <= 15) {
policy.service_level = sl;
} else {
LOG(WARNING) << "Ignore service_level in policy " << policy.name
<< ", value " << sl << " out of range (0-15)";
}
}
if (policy_json.contains("traffic_class")) {
int tc = policy_json.value("traffic_class", -1);
if (tc >= 0 && tc <= 255) {
policy.traffic_class = tc;
} else {
LOG(WARNING) << "Ignore traffic_class in policy " << policy.name
<< ", value " << tc << " out of range (0-255)";
}
}
// Reserved for step 2 (per-class QP pools); parsed for forward schema
// compatibility, no effect yet.
if (policy_json.contains("qp_pool")) {
auto& qp = policy_json["qp_pool"];
if (qp.is_string()) policy.qp_pool = qp.get<std::string>();
}
Comment on lines +212 to +235

@gemini-code-assist gemini-code-assist Bot Jun 26, 2026

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medium

Using nlohmann::json::value() or direct retrieval on keys without type checking can throw a nlohmann::json::type_error exception if the value in the JSON configuration has an unexpected type (e.g., a string, boolean, or null). To ensure that a bad configuration never breaks selection or crashes the application, we should explicitly check the type using is_number_integer() before retrieving the value. Additionally, we should log a warning if qp_pool is present but is not a string, for consistency.

        if (policy_json.contains("service_level")) {
            auto& sl_val = policy_json["service_level"];
            if (sl_val.is_number_integer()) {
                int sl = sl_val.get<int>();
                if (sl >= 0 && sl <= 15) {
                    policy.service_level = sl;
                } else {
                    LOG(WARNING) << "Ignore service_level in policy " << policy.name
                                 << ", value " << sl << " out of range (0-15)";
                }
            } else {
                LOG(WARNING) << "Ignore service_level in policy " << policy.name
                             << ", value is not an integer";
            }
        }
        if (policy_json.contains("traffic_class")) {
            auto& tc_val = policy_json["traffic_class"];
            if (tc_val.is_number_integer()) {
                int tc = tc_val.get<int>();
                if (tc >= 0 && tc <= 255) {
                    policy.traffic_class = tc;
                } else {
                    LOG(WARNING) << "Ignore traffic_class in policy " << policy.name
                                 << ", value " << tc << " out of range (0-255)";
                }
            } else {
                LOG(WARNING) << "Ignore traffic_class in policy " << policy.name
                             << ", value is not an integer";
            }
        }
        // Reserved for step 2 (per-class QP pools); parsed for forward schema
        // compatibility, no effect yet.
        if (policy_json.contains("qp_pool")) {
            auto& qp = policy_json["qp_pool"];
            if (qp.is_string()) {
                policy.qp_pool = qp.get<std::string>();
            } else {
                LOG(WARNING) << "Ignore qp_pool in policy " << policy.name
                             << ", value is not a string";
            }
        }

Comment on lines +232 to +235

@staryxchen staryxchen Jun 26, 2026

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Empty-string qp_pool is treated as set, which is semantically different from nullopt (= use default pool).

Comment on lines +232 to +235

@staryxchen staryxchen Jun 26, 2026

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SL/TC out-of-range gets a LOG(WARNING), but "qp_pool": 42 (non-string) is silently no-op'd. For schema consistency, log a warning here too, you don't want a typo'd config to look like it took effect when it didn't.


policies_.push_back(std::move(policy));
LOG(INFO) << "Loaded transport policy: " << policy.name
<< " (segment_type=" << segment_type_str
Expand Down Expand Up @@ -384,6 +412,13 @@ SelectionResult TransportSelector::select(
return result; // UNSPEC, all devices
}

// Carry the matched policy's link-layer QoS out to the caller (RFC #2519 /
// #2568, step 1). These are plumbed but not yet applied at QP setup; that
// is the per-class QP pool follow-up (step 2).
result.service_level = matching_policy->service_level;
result.traffic_class = matching_policy->traffic_class;
result.qp_pool = matching_policy->qp_pool;

// Convert device names to mask
result.device_mask = ~0ULL; // Default: all devices
if (!matching_policy->devices.empty() && topology_) {
Expand Down
71 changes: 71 additions & 0 deletions mooncake-transfer-engine/tent/tests/transport_selector_test.cpp
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Expand Up @@ -641,6 +641,77 @@ TEST(TransportSelectorTest, HintNotInMatchingPolicyReturnsUnspec) {
EXPECT_EQ(r.transport, UNSPEC);
}

// RFC #2519 / #2568 step 1: a policy's link-layer QoS (service_level /
// traffic_class / qp_pool) is parsed from JSON and carried out via
// SelectionResult. (Step 1 only plumbs the values; applying them at QP setup
// is the per-class QP pool follow-up.)
TEST(TransportSelectorTest, PolicyLinkLayerQoSIsParsedAndCarried) {
auto conf = std::make_shared<Config>();
json policy;
policy["name"] = "kv-critical";
policy["segment_type"] = "memory";
policy["transports"] = {"rdma"};
policy["service_level"] = 3;
policy["traffic_class"] = 96;
policy["qp_pool"] = "kv";
conf->set("policy", json::array({policy}));

TransportSelector selector(conf);
std::array<std::shared_ptr<Transport>, kSupportedTransportTypes>
transports{};
transports[RDMA] = std::make_shared<FakeTransport>(RDMA);
static_cast<FakeTransport*>(transports[RDMA].get())->setDramToDram(true);

std::vector<TransportType> buffer_transports = {RDMA};
SelectionContext ctx;
ctx.segment_type = SegmentType::Memory;
ctx.same_machine = false;
ctx.local_memory_type = MTYPE_CPU;
ctx.remote_memory_type = MTYPE_CPU;
ctx.buffer_transports = &buffer_transports;
ctx.policy_name = "kv-critical";

auto r = selector.select(ctx, transports, /*index=*/0);
ASSERT_TRUE(r.service_level.has_value());
EXPECT_EQ(r.service_level.value(), 3);
ASSERT_TRUE(r.traffic_class.has_value());
EXPECT_EQ(r.traffic_class.value(), 96);
ASSERT_TRUE(r.qp_pool.has_value());
EXPECT_EQ(r.qp_pool.value(), "kv");
}

// Out-of-range SL/TC are ignored (left as nullopt) so a bad config never
// changes selection behavior.
TEST(TransportSelectorTest, PolicyLinkLayerQoSOutOfRangeIgnored) {
auto conf = std::make_shared<Config>();
json policy;
policy["name"] = "bad-qos";
policy["segment_type"] = "memory";
policy["transports"] = {"rdma"};
policy["service_level"] = 99; // > 15, invalid
policy["traffic_class"] = 9999; // > 255, invalid
conf->set("policy", json::array({policy}));

TransportSelector selector(conf);
std::array<std::shared_ptr<Transport>, kSupportedTransportTypes>
transports{};
transports[RDMA] = std::make_shared<FakeTransport>(RDMA);
static_cast<FakeTransport*>(transports[RDMA].get())->setDramToDram(true);

std::vector<TransportType> buffer_transports = {RDMA};
SelectionContext ctx;
ctx.segment_type = SegmentType::Memory;
ctx.same_machine = false;
ctx.local_memory_type = MTYPE_CPU;
ctx.remote_memory_type = MTYPE_CPU;
ctx.buffer_transports = &buffer_transports;
ctx.policy_name = "bad-qos";

auto r = selector.select(ctx, transports, /*index=*/0);
EXPECT_FALSE(r.service_level.has_value());
EXPECT_FALSE(r.traffic_class.has_value());
}

} // namespace
} // namespace tent
} // namespace mooncake
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