scx_rustland_core: Use RingBuffer:consume_raw_n()

Update libbpf-rs to use the consume_raw_n() API to consume tasks from
the BPF ring buffer.

Signed-off-by: Andrea Righi <arighi@nvidia.com>

Author: arighi

Cargo.lock

@@ -138,7 +138,7 @@ if should_build_libbpf
   endforeach
 
   message('Fetching libbpf repo')
-  libbpf_commit = 'c5f22aca0f3aa855daa159b2777472b35e721804'
+  libbpf_commit = '02bdeb7a2c2e7cb2c9cecb125527a9c5a6bbf139'
   run_command(fetch_libbpf, meson.current_build_dir(), libbpf_commit, check: true)
 
   make_jobs = 1

meson.build

@@ -10,7 +10,7 @@ description = "Framework to implement sched_ext schedulers running in user space
 [dependencies]
 anyhow = "1.0.65"
 plain = "0.2.3"
-libbpf-rs = "=0.25.0-beta.1"
+libbpf-rs = { git = "https://github.com/arighi/libbpf-rs", branch = "consume-raw-n" }
 libc = "0.2.137"
 seccomp = "0.1"
 scx_utils = { path = "../scx_utils", version = "1.0.15" }

rust/scx_rustland_core/Cargo.toml

@@ -169,10 +169,6 @@ struct AlignedBuffer([u8; BUFSIZE]);
 
 static mut BUF: AlignedBuffer = AlignedBuffer([0; BUFSIZE]);
 
-// Special negative error code for libbpf to stop after consuming just one item from a BPF
-// ring buffer.
-const LIBBPF_STOP: i32 = -255;
-
 static SET_HANDLER: Once = Once::new();
 
 fn set_ctrlc_handler(shutdown: Arc<AtomicBool>) -> Result<(), anyhow::Error> {
@@ -224,18 +220,8 @@ impl<'cb> BpfScheduler<'cb> {
                 BUF.0.copy_from_slice(data);
             }
 
-            // Return an unsupported error to stop early and consume only one item.
-            //
-            // NOTE: this is quite a hack. I wish libbpf would honor stopping after the first item
-            // is consumed, upon returning a non-zero positive value here, but it doesn't seem to
-            // be the case:
-            //
-            // https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/lib/bpf/ringbuf.c?h=v6.8-rc5#n260
-            //
-            // Maybe we should fix this to stop processing items from the ring buffer also when a
-            // value > 0 is returned.
-            //
-            LIBBPF_STOP
+            // Return 0 to indicate successful completion of the copy.
+            0
         }
 
         // Check host topology to determine if we need to enable SMT capabilities.
@@ -511,12 +497,12 @@ impl<'cb> BpfScheduler<'cb> {
     // Receive a task to be scheduled from the BPF dispatcher.
     #[allow(static_mut_refs)]
     pub fn dequeue_task(&mut self) -> Result<Option<QueuedTask>, i32> {
-        match self.queued.consume_raw() {
+        match self.queued.consume_raw_n(1) {
             0 => {
                 self.skel.maps.bss_data.nr_queued = 0;
                 Ok(None)
             }
-            LIBBPF_STOP => {
+            1 => {
                 // A valid task is received, convert data to a proper task struct.
                 let task = unsafe { EnqueuedMessage::from_bytes(&BUF.0).to_queued_task() };
                 self.skel.maps.bss_data.nr_queued =

rust/scx_rustland_core/assets/bpf.rs

@@ -14,7 +14,7 @@ bindgen = ">=0.69"
 glob = "0.3.2"
 hex = "0.4.3"
 lazy_static = "1.5.0"
-libbpf-sys = "=1.4.6"
+libbpf-sys = "1.5.1"
 libbpf-cargo = "=0.25.0-beta.1"
 libbpf-rs = "=0.25.0-beta.1"
 log = "0.4.17"

rust/scx_utils/Cargo.toml

@@ -10,7 +10,7 @@ license = "GPL-2.0-only"
 anyhow = "1.0.65"
 plain = "0.2.3"
 ctrlc = { version = "3.1", features = ["termination"] }
-libbpf-rs = "=0.25.0-beta.1"
+libbpf-rs = { git = "https://github.com/arighi/libbpf-rs", branch = "consume-raw-n" }
 libc = "0.2.137"
 scx_utils = { path = "../../../rust/scx_utils", version = "1.0.15" }
 scx_rustland_core = { path = "../../../rust/scx_rustland_core", version = "2.3.1" }

scheds/rust/scx_rlfifo/Cargo.toml

@@ -12,7 +12,7 @@ plain = "0.2.3"
 clap = { version = "4.5.28", features = ["derive", "env", "unicode", "wrap_help"] }
 ctrlc = { version = "3.1", features = ["termination"] }
 fb_procfs = "0.7"
-libbpf-rs = "=0.25.0-beta.1"
+libbpf-rs = { git = "https://github.com/arighi/libbpf-rs", branch = "consume-raw-n" }
 libc = "0.2.137"
 log = "0.4.17"
 ordered-float = "3.4.0"