make BPF non-optional on Linux (#336)

Changes BPF to be non-optional on Linux. Drops fall-back samplers
so that metric provenance is clear and so sampler overhead is
consistent.

.github/workflows/cargo.yml

@@ -101,7 +101,6 @@ jobs:
       matrix:
         os: [ ubuntu-latest, ubuntu-20.04, macos-latest ]
         profile: [ release, debug ]
-        features: [ default, no-default ]
     steps:
       - uses: actions/checkout@v3
       - uses: ./.github/actions/setup-rust
@@ -118,15 +117,6 @@ jobs:
         run: echo 'FLAGS=' >> $GITHUB_ENV
         shell: bash
 
-      - name: Update feature flags
-        if: ${{ matrix.features == 'default' }}
-        run: echo 'FEATURE_FLAGS=--features default' >> $GITHUB_ENV
-        shell: bash
-      - name: Update feature flags
-        if: ${{ matrix.features == 'no-default' }}
-        run: echo 'FEATURE_FLAGS=--no-default-features' >> $GITHUB_ENV
-        shell: bash
-
       - name: Install dependencies
         if: ${{ matrix.os != 'macos-latest' }}
         shell: bash

CHANGELOG.md

@@ -1,5 +1,9 @@
 ## [Unreleased]
 
+### Changed
+
+- BPF is now non-optional on Linux. (#336)
+
 ## [3.18.1] - 2024-08-09
 
 ### Changed

Cargo.toml

@@ -7,7 +7,7 @@ edition = "2021"
 description = "High resolution systems performance telemetry agent"
 
 [workspace.package]
-version = "3.18.2-alpha.11"
+version = "4.0.0-alpha.1"
 license = "MIT OR Apache-2.0"
 
 [dependencies]
@@ -41,18 +41,13 @@ async-trait = "0.1.81"
 parking_lot = "0.12.3"
 
 [target.'cfg(target_os = "linux")'.dependencies]
-libbpf-rs = { version = "0.24.2", optional = true }
-libbpf-sys = { version = "1.4.3", optional = true }
+libbpf-rs = { version = "0.24.2" }
+libbpf-sys = { version = "1.4.3" }
 perf-event2 = "0.7.2"
 nvml-wrapper = "0.9.0"
 
 [target.'cfg(target_os = "linux")'.build-dependencies]
-libbpf-cargo = { version = "0.24.2", optional = true }
-
-[features]
-all = ["bpf"]
-default = ["bpf"]
-bpf = ["libbpf-cargo","libbpf-rs","libbpf-sys"]
+libbpf-cargo = { version = "0.24.2" }
 
 [profile.bench]
 debug = true

build.rs

@@ -1,9 +1,9 @@
 fn main() {
-    #[cfg(all(feature = "bpf", target_os = "linux"))]
+    #[cfg(target_os = "linux")]
     bpf::generate();
 }
 
-#[cfg(all(feature = "bpf", target_os = "linux"))]
+#[cfg(target_os = "linux")]
 mod bpf {
     use libbpf_cargo::SkeletonBuilder;
 

config.toml

@@ -61,10 +61,6 @@ histogram_grouping_power = 4
 # collection for that sampler. Setting the default to false requires that
 # individual sampler configs are used to opt-in to collection.
 enabled = true
-# Controls whether BPF sampler will be used. When a metric can be collected
-# without BPF, that sampler will be used instead. Otherwise, the sampler will
-# effectively be disabled.
-bpf = true
 # The collection interval for the sampler. Shorter intervals result in less
 # error when calculating rates and allow for more accurately capturing bursts in
 # the related percentile metrics.
@@ -83,17 +79,14 @@ enabled = true
 [samplers.block_io_requests]
 enabled = true
 
-# Instruments CPU frequency, instructions, and cycles using BPF perf events or
-# frequency only via /proc/cpuinfo
+# Instruments CPU frequency, instructions, and cycles using perf events
 [samplers.cpu_perf]
 enabled = true
-bpf = true
 
-# Instruments CPU usage by state with BPF or by reading /proc/stat on linux
+# Instruments CPU usage by state with BPF
 # On macos host_processor_info() is used
 [samplers.cpu_usage]
 enabled = true
-bpf = true
 
 # Instruments the number of currently open file descriptors using
 # /proc/sys/fs/file-nr
@@ -161,8 +154,7 @@ enabled = true
 [samplers.tcp_retransmit]
 enabled = true
 
-# Samples TCP traffic using either a BPF sampler or /proc/net/snmp to provide
-# metrics for TX/RX bytes and packets
+# Samples TCP traffic using a BPF sampler to get metrics for TX/RX bytes and
+# packets
 [samplers.tcp_traffic]
 enabled = true
-bpf = true

src/common/mod.rs

@@ -1,4 +1,4 @@
-#[cfg(all(feature = "bpf", target_os = "linux"))]
+#[cfg(target_os = "linux")]
 pub mod bpf;
 
 pub mod classic;

src/config/mod.rs

@@ -76,13 +76,6 @@ impl Config {
             .unwrap_or(self.defaults.enabled.unwrap_or(enabled()))
     }
 
-    pub fn bpf(&self, name: &str) -> bool {
-        self.samplers
-            .get(name)
-            .and_then(|v| v.bpf)
-            .unwrap_or(self.defaults.bpf.unwrap_or(enabled()))
-    }
-
     pub fn interval(&self, name: &str) -> Duration {
         let interval = self
             .samplers
@@ -261,8 +254,6 @@ pub struct SamplerConfig {
     #[serde(default)]
     enabled: Option<bool>,
     #[serde(default)]
-    bpf: Option<bool>,
-    #[serde(default)]
     interval: Option<String>,
 }
 

src/samplers/block_io/linux/latency/mod.rs

@@ -21,7 +21,7 @@ use crate::*;
 #[distributed_slice(ASYNC_SAMPLERS)]
 fn spawn(config: Arc<Config>, runtime: &Runtime) {
     // check if sampler should be enabled
-    if !(config.enabled(NAME) && config.bpf(NAME)) {
+    if !config.enabled(NAME) {
         return;
     }
 

src/samplers/block_io/linux/mod.rs

@@ -1,5 +1,2 @@
-#[cfg(feature = "bpf")]
 mod latency;
-
-#[cfg(feature = "bpf")]
 mod requests;

src/samplers/block_io/linux/requests/mod.rs

@@ -22,7 +22,7 @@ use crate::*;
 #[distributed_slice(ASYNC_SAMPLERS)]
 fn spawn(config: Arc<Config>, runtime: &Runtime) {
     // check if sampler should be enabled
-    if !(config.enabled(NAME) && config.bpf(NAME)) {
+    if !config.enabled(NAME) {
         return;
     }
 

src/samplers/cpu/linux/perf/mod.rs

@@ -9,21 +9,13 @@ use perf_event::{Builder, ReadFormat};
 use samplers::hwinfo::hardware_info;
 
 mod perf_group;
-mod proc_cpuinfo;
 
 use perf_group::*;
-use proc_cpuinfo::*;
 
 #[distributed_slice(SAMPLERS)]
 fn init(config: Arc<Config>) -> Box<dyn Sampler> {
-    // try to initialize the perf counter based sampler that provides more info
-    // with lower overhead
     if let Ok(perf) = Perf::new(config.clone()) {
         Box::new(perf)
-    // try to fallback to the /proc/cpuinfo based sampler if perf events are not
-    // supported
-    } else if let Ok(cpuinfo) = ProcCpuinfo::new(config) {
-        Box::new(cpuinfo)
     } else {
         Box::new(Nop {})
     }
@@ -41,7 +33,7 @@ pub struct Perf {
 impl Perf {
     pub fn new(config: Arc<Config>) -> Result<Self, ()> {
         // check if sampler should be enabled
-        if !(config.enabled(NAME) && config.bpf(NAME)) {
+        if !config.enabled(NAME) {
             return Err(());
         }
 

src/samplers/cpu/linux/usage/bpf.rs

@@ -130,7 +130,7 @@ impl OnlineCores {
 impl CpuUsage {
     pub fn new(config: Arc<Config>) -> Result<Self, ()> {
         // check if sampler should be enabled
-        if !(config.enabled(NAME) && config.bpf(NAME)) {
+        if !config.enabled(NAME) {
             return Err(());
         }
 

src/samplers/cpu/linux/usage/mod.rs

@@ -3,37 +3,14 @@ use crate::*;
 
 const NAME: &str = "cpu_usage";
 
-#[cfg(feature = "bpf")]
 mod bpf;
 
-mod proc_stat;
-
-#[cfg(feature = "bpf")]
 use bpf::*;
 
-use proc_stat::*;
-
-#[cfg(feature = "bpf")]
 #[distributed_slice(SAMPLERS)]
 fn init(config: Arc<Config>) -> Box<dyn Sampler> {
-    // try to initialize the bpf based sampler
     if let Ok(s) = CpuUsage::new(config.clone()) {
         Box::new(s)
-    // try to fallback to the /proc/stat based sampler if there was an error
-    } else if let Ok(s) = ProcStat::new(config) {
-        Box::new(s)
-    } else {
-        Box::new(Nop {})
-    }
-}
-
-#[cfg(not(feature = "bpf"))]
-#[distributed_slice(SAMPLERS)]
-fn init(config: Arc<Config>) -> Box<dyn Sampler> {
-    // try to use the /proc/stat based sampler since BPF was not enabled for
-    // this build
-    if let Ok(s) = ProcStat::new(config) {
-        Box::new(s)
     } else {
         Box::new(Nop {})
     }