Changeset 34b61882 for libcfa/src/concurrency

Timestamp:

Jul 8, 2020, 6:05:11 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:

732b406

Parents:

1d5e4711

Message:

Submission release is now based on previous seen head rather than the return value of io_uring_enter
This will make it easier to support SQ POLLING
It is not currently thread safe.
It is unclear if it can be made thread safe

File:

• libcfa/src/concurrency/io.cfa (modified) (10 diffs)

libcfa/src/concurrency/io.cfa

@@ -109 +109 @@
                 volatile uint32_t * head;
                 volatile uint32_t * tail;
+                volatile uint32_t prev_head;
 
                 // The actual kernel ring which uses head/tail
@@ -259 +260 @@
                 sq.dropped = (         uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.dropped);
                 sq.array   = (         uint32_t *)(((intptr_t)sq.ring_ptr) + params.sq_off.array);
+                sq.prev_head = *sq.head;
 
                 {
@@ -430 +432 @@
 //=============================================================================================
         static unsigned __collect_submitions( struct __io_data & ring );
+        static uint32_t __release_consumed_submission( struct __io_data & ring );
 
         // Process a single completion message from the io_uring
@@ -444 +447 @@
 
                 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 ) {
@@ -457 +459 @@
 
                         // 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;
-                        }
+                        __release_consumed_submission( ring );
 
                         // update statistics
@@ -738 +737 @@
 
                         block++;
-                        yield();
+                        if( try_lock(ring.submit_q.lock __cfaabi_dbg_ctx2) ) {
+                                __release_consumed_submission( ring );
+                                unlock( ring.submit_q.lock );
+                        }
+                        else {
+                                yield();
+                        }
                 }
 
@@ -794 +799 @@
                         // We got the lock
                         unsigned to_submit = __collect_submitions( ring );
-                        uint32_t shead = *ring.submit_q.head;
                         int ret = syscall( __NR_io_uring_enter, ring.fd, to_submit, 0, 0, 0p, _NSIG / 8);
                         if( ret < 0 ) {
@@ -810 +814 @@
 
                         // 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 ];
-                                ring.submit_q.sqes[ idx ].user_data = 0;
-                        }
+                        __release_consumed_submission( ring );
 
                         // update statistics
@@ -851 +851 @@
                         )
 
-                        ring.submit_q.sqes[ idx & mask ].user_data = 0;
+                        // Release the consumed SQEs
+                        __release_consumed_submission( ring );
 
                         unlock(ring.submit_q.lock);
@@ -885 +886 @@
                 return to_submit;
         }
+
+        static uint32_t __release_consumed_submission( struct __io_data & ring ) {
+                const uint32_t smask = *ring.submit_q.mask;
+                uint32_t chead = *ring.submit_q.head;
+                uint32_t phead = ring.submit_q.prev_head;
+                ring.submit_q.prev_head = chead;
+                uint32_t count = chead - phead;
+                for( i; count ) {
+                        uint32_t idx = ring.submit_q.array[ (phead + i) & smask ];
+                        ring.submit_q.sqes[ idx ].user_data = 0;
+                }
+                return count;
+        }
 #endif