Performance issue with micrometer and otel baggage

Describe the bug
I'm attempting to add several OpenTelemetry baggage items to the current tracing context using Micrometer and OpenTelemetry in a spring-cloud-starter-gateway-server-webflux application, but this appears to be significantly impacting throughput. It degrades from ~108 RPS to ~51 RPS 😟

Before baggage:

After baggage:

I have followed the steps given in the micrometer documentation page, i.e. by using ReactorBaggage and ObservationAwareBaggageThreadLocalAccessor

see here - https://docs.micrometer.io/tracing/reference/configuring.html#_context_propagation_with_micrometer_tracing

Sample

id("org.springframework.boot") version "3.5.0"
id("io.spring.dependency-management") version "1.1.7"

extra["springCloudVersion"] = "2025.0.0"


implementation("io.micrometer:micrometer-tracing")
implementation("io.micrometer:micrometer-tracing-bridge-otel")

Registering ObservationAwareBaggageThreadLocalAccessor:

@Bean
    fun otelWebFilter(
        tracer: Tracer,
        registry: ObservationRegistry,
    ): OtelWebFilter {
        ContextRegistry.getInstance()
            .registerThreadLocalAccessor(ObservationAwareBaggageThreadLocalAccessor(registry, tracer))
        ContextRegistry.getInstance().registerThreadLocalAccessor(ObservationAwareSpanThreadLocalAccessor(tracer))
        return OtelWebFilter(tracer)
    }

ReactorBaggage with contextWrite:

class OtelWebFilter(private val tracer: Tracer) : WebFilter {

    private val logger = LoggerFactory.getLogger(OtelWebFilter::class.java)

    override fun filter(
        exchange: ServerWebExchange,
        chain: WebFilterChain
    ): Mono<Void> {
        val baggage = mapOf(
            "username" to exchange.request.headers.getFirst("X-Username").orEmpty(),
            "tenantId" to exchange.request.headers.getFirst("X-Tenant-Id").orEmpty(),
        )
        return chain.filter(exchange)
            .doOnSubscribe { logger.debug("Setting baggage for path: {}", exchange.request.path) }
            .doOnSuccess { logger.debug("Setting baggage completed") }
            .contextWrite(ReactorBaggage.append(baggage))
    }
}

Please look into it and let me know if you need further details

Reproduce the report with the Kotlin Spring Cloud Gateway sample, starting at the OtelWebFilter, ReactorBaggage.contextWrite call, and registered ObservationAware baggage accessors. Compare throughput with and without baggage and context propagation; done means the performance cause is isolated and a validated fix or clear finding is reported.