fscache: enable multi-threading to process fscache requests

Add command line option "fscache-threads" to nydusd to support
multi-threading for fscache service. There's one thread to receive
fscache request from cachefile fd, and dispatch `READ` requests to
multiple working threads through a multi-producer, multi-consumer
channel.

We have observed about 40% performance boost when serving some multi
threading container workloads.

Signed-off-by: Jiang Liu <gerry@linux.alibaba.com>

src/bin/nydusd/fs_cache.rs

@@ -223,6 +223,7 @@ struct FsCacheState {
 pub struct FsCacheHandler {
     active: AtomicBool,
     barrier: Barrier,
+    threads: usize,
     file: File,
     state: Arc<Mutex<FsCacheState>>,
     poller: Mutex<Poll>,
@@ -236,6 +237,7 @@ impl FsCacheHandler {
         dir: &str,
         tag: Option<&str>,
         blob_cache_mgr: Arc<BlobCacheMgr>,
+        threads: usize,
     ) -> Result<Self> {
         info!(
             "fscache: create FsCacheHandler with dir {}, tag {}",
@@ -279,14 +281,20 @@ impl FsCacheHandler {
 
         Ok(FsCacheHandler {
             active: AtomicBool::new(true),
-            barrier: Barrier::new(2),
+            barrier: Barrier::new(threads + 1),
+            threads,
             file,
             state: Arc::new(Mutex::new(state)),
             poller: Mutex::new(poller),
             waker: Arc::new(waker),
         })
     }
 
+    /// Get number of working threads to service fscache requests.
+    pub fn working_threads(&self) -> usize {
+        self.threads
+    }
+
     /// Stop worker threads for the fscache service.
     pub fn stop(&self) {
         self.active.store(false, Ordering::Release);
@@ -327,6 +335,8 @@ impl FsCacheHandler {
                     && event.token() == Token(TOKEN_EVENT_WAKER)
                     && !self.active.load(Ordering::Acquire)
                 {
+                    // Notify next worker to exit.
+                    let _ = self.waker.wake();
                     self.barrier.wait();
                     return Ok(());
                 }

src/bin/nydusd/main.rs

@@ -343,6 +343,26 @@ fn append_services_subcmd_options(app: App<'static, 'static>) -> App<'static, 's
                 .help("Tag to identify the fscache daemon instance")
                 .takes_value(true)
                 .requires("fscache"),
+        )
+        .arg(
+            Arg::with_name("fscache-threads")
+                .long("fscache-threads")
+                .default_value("1")
+                .help("Number of working threads to serve fscache requests")
+                .takes_value(true)
+                .required(false)
+                .validator(|v| {
+                    if let Ok(t) = v.parse::<i32>() {
+                        if t > 0 && t <= 1024 {
+                            Ok(())
+                        } else {
+                            Err("Invalid working thread number {}, valid values: [1-1024]"
+                                .to_string())
+                        }
+                    } else {
+                        Err("Input thread number is invalid".to_string())
+                    }
+                }),
         );
 
     app.subcommand(subcmd)

src/bin/nydusd/service_controller.rs

@@ -43,15 +43,18 @@ impl ServiceController {
         #[cfg(target_os = "linux")]
         if self.fscache_enabled.load(Ordering::Acquire) {
             if let Some(fscache) = self.fscache.lock().unwrap().clone() {
-                std::thread::spawn(move || {
-                    if let Err(e) = fscache.run_loop() {
-                        error!("Failed to run fscache service loop, {}", e);
-                    }
-                    // Notify the global service controller that one working thread is exiting.
-                    if let Err(e) = crate::DAEMON_CONTROLLER.waker.wake() {
-                        error!("Failed to notify the global service controller, {}", e);
-                    }
-                });
+                for _ in 0..fscache.working_threads() {
+                    let fscache2 = fscache.clone();
+                    std::thread::spawn(move || {
+                        if let Err(e) = fscache2.run_loop() {
+                            error!("Failed to run fscache service loop, {}", e);
+                        }
+                        // Notify the global service controller that one working thread is exiting.
+                        if let Err(e) = crate::DAEMON_CONTROLLER.waker.wake() {
+                            error!("Failed to notify the global service controller, {}", e);
+                        }
+                    });
+                }
             }
         }
 
@@ -117,16 +120,33 @@ impl ServiceController {
         };
         let tag = subargs.value_of("fscache-tag");
 
+        let mut threads = 1usize;
+        if let Some(threads_value) = subargs.value_of("fscache-threads") {
+            if let Ok(t) = threads_value.parse::<i32>() {
+                if t > 0 && t <= 1024 {
+                    threads = t as usize;
+                } else {
+                    return Err(einval!(
+                        "Invalid working thread number {}, valid values: [1-1024]"
+                    ));
+                }
+            } else {
+                return Err(einval!("Input thread number is invalid".to_string()));
+            }
+        }
+
         info!(
-            "Create fscache instance at {} with tag {}",
+            "Create fscache instance at {} with tag {}, {} working threads",
             p,
-            tag.unwrap_or("<none>")
+            tag.clone().unwrap_or("<none>"),
+            threads
         );
         let fscache = crate::fs_cache::FsCacheHandler::new(
             "/dev/cachefiles",
             p,
             tag,
             self.blob_cache_mgr.clone(),
+            threads,
         )?;
         *self.fscache.lock().unwrap() = Some(Arc::new(fscache));
         self.fscache_enabled.store(true, Ordering::Release);