Changeset 1d5e4711 for libcfa/src/concurrency/io.cfa

Timestamp:

Jul 8, 2020, 4:30:14 PM (4 years ago)

Author:

Thierry Delisle <tdelisle@…>

Branches:

ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, master, new-ast, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

34b61882

Parents:

1c49dc5

Message:

Optim: No longer call io_uring_enter to poll for events if

• We don't want to block
• There is nothing to submit

This is only valid for "interrupt driven I/O", polling driven I/O not yet supported.

File:

• libcfa/src/concurrency/io.cfa (modified) (6 diffs)

libcfa/src/concurrency/io.cfa

@@ -429 +429 @@
 // I/O Polling
 //=============================================================================================
+        static unsigned __collect_submitions( struct __io_data & ring );
+
         // Process a single completion message from the io_uring
         // This is NOT thread-safe
-        static unsigned __collect_submitions( struct __io_data & ring );
         static [int, bool] __drain_io( & struct __io_data ring, * sigset_t mask, int waitcnt, bool in_kernel ) {
                 /* paranoid */ verify( !kernelTLS.preemption_state.enabled );
+                const uint32_t smask = *ring.submit_q.mask;
 
                 unsigned to_submit = 0;
@@ -441 +443 @@
                 }
 
-                const uint32_t smask = *ring.submit_q.mask;
-                uint32_t shead = *ring.submit_q.head;
-                int ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, waitcnt, IORING_ENTER_GETEVENTS, mask, _NSIG / 8);
-                if( ret < 0 ) {
-                        switch((int)errno) {
-                        case EAGAIN:
-                        case EINTR:
-                                return [0, true];
-                        default:
-                                abort( "KERNEL ERROR: IO_URING WAIT - %s\n", strerror(errno) );
-                        }
-                }
-
-                // Release the consumed SQEs
-                for( i; ret ) {
-                        uint32_t idx = ring.submit_q.array[ (i + shead) & smask ];
-                        ring.submit_q.sqes[ idx ].user_data = 0;
-                }
-
-                // update statistics
-                __STATS__( true,
-                        if( to_submit > 0 ) {
-                                io.submit_q.submit_avg.rdy += to_submit;
-                                io.submit_q.submit_avg.csm += ret;
-                                io.submit_q.submit_avg.cnt += 1;
-                        }
-                )
+                if (to_submit > 0 || waitcnt > 0) {
+                        uint32_t shead = *ring.submit_q.head;
+                        int ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, waitcnt, IORING_ENTER_GETEVENTS, mask, _NSIG / 8);
+                        if( ret < 0 ) {
+                                switch((int)errno) {
+                                case EAGAIN:
+                                case EINTR:
+                                        return [0, true];
+                                default:
+                                        abort( "KERNEL ERROR: IO_URING WAIT - %s\n", strerror(errno) );
+                                }
+                        }
+
+                        // Release the consumed SQEs
+                        for( i; ret ) {
+                                uint32_t idx = ring.submit_q.array[ (i + shead) & smask ];
+                                ring.submit_q.sqes[ idx ].user_data = 0;
+                        }
+
+                        // update statistics
+                        __STATS__( true,
+                                if( to_submit > 0 ) {
+                                        io.submit_q.submit_avg.rdy += to_submit;
+                                        io.submit_q.submit_avg.csm += ret;
+                                        io.submit_q.submit_avg.cnt += 1;
+                                }
+                        )
+                }
+
+                // Memory barrier
+                __atomic_thread_fence( __ATOMIC_SEQ_CST );
 
                 // Drain the queue
@@ -474 +480 @@
                 const uint32_t mask = *ring.completion_q.mask;
 
-                // Memory barrier
-                __atomic_thread_fence( __ATOMIC_SEQ_CST );
-
                 // Nothing was new return 0
                 if (head == tail) {
@@ -483 +486 @@
 
                 uint32_t count = tail - head;
+                /* paranoid */ verify( count != 0 );
                 for(i; count) {
                         unsigned idx = (head + i) & mask;
@@ -790 +794 @@
                         // We got the lock
                         unsigned to_submit = __collect_submitions( ring );
-                        const uint32_t smask = *ring.submit_q.mask;
                         uint32_t shead = *ring.submit_q.head;
                         int ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, 0, 0, 0p, _NSIG / 8);
@@ -807 +810 @@
 
                         // Release the consumed SQEs
+                        const uint32_t smask = *ring.submit_q.mask;
                         for( i; ret ) {
                                 uint32_t idx = ring.submit_q.array[ (i + shead) & smask ];