fio: document locking for overlap checking in offload mode

Overlap checking in offload submission mode uses locks in an unusual
manner. Add some comments in the code to clarify how locks are used.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/backend.c b/backend.c
index 1c60138c50b5a957b35378368734b83e906baf92..d6450baf1efdef1da5945445e7f9325c2e7f0efd 100644 (file)
--- a/backend.c
+++ b/backend.c
@@ -1874,6 +1874,11 @@ static void *thread_main(void *data)
                         "perhaps try --debug=io option for details?\n",
                         td->o.name, td->io_ops->name);
 
                         "perhaps try --debug=io option for details?\n",
                         td->o.name, td->io_ops->name);
 

+       /*
+        * Acquire this lock if we were doing overlap checking in
+        * offload mode so that we don't clean up this job while
+        * another thread is checking its io_u's for overlap
+        */

        if (td_offload_overlap(td))
                pthread_mutex_lock(&overlap_check);
        td_set_runstate(td, TD_FINISHING);
        if (td_offload_overlap(td))
                pthread_mutex_lock(&overlap_check);
        td_set_runstate(td, TD_FINISHING);

diff --git a/ioengines.c b/ioengines.c
index 56723addc5af2f57348d2b3784c4594a5c8e88b1..b7df860825e55bb433b20a981f45c2ebf6439734 100644 (file)
--- a/ioengines.c
+++ b/ioengines.c
@@ -288,6 +288,13 @@ enum fio_q_status td_io_queue(struct thread_data *td, struct io_u *io_u)
 
        assert((io_u->flags & IO_U_F_FLIGHT) == 0);
        io_u_set(td, io_u, IO_U_F_FLIGHT);
 
        assert((io_u->flags & IO_U_F_FLIGHT) == 0);
        io_u_set(td, io_u, IO_U_F_FLIGHT);

+
+       /*
+        * If overlap checking was enabled in offload mode we
+        * can release this lock that was acquired when we
+        * started the overlap check because the IO_U_F_FLIGHT
+        * flag is now set
+        */

        if (td_offload_overlap(td))
                pthread_mutex_unlock(&overlap_check);
 
        if (td_offload_overlap(td))
                pthread_mutex_unlock(&overlap_check);
 

diff --git a/rate-submit.c b/rate-submit.c
index 68ad755d948056c0ff9fabc0a26a14961f410a05..e5c6204351db00304db32fa376837faa9c420cc9 100644 (file)
--- a/rate-submit.c
+++ b/rate-submit.c
@@ -21,6 +21,14 @@ static void check_overlap(struct io_u *io_u)
                 * time to prevent two threads from thinking the coast
                 * is clear and then submitting IOs that overlap with
                 * each other
                 * time to prevent two threads from thinking the coast
                 * is clear and then submitting IOs that overlap with
                 * each other

+                *
+                * If an overlap is found, release the lock and
+                * re-acquire it before checking again to give other
+                * threads a chance to make progress
+                *
+                * If an overlap is not found, release the lock when the
+                * io_u's IO_U_F_FLIGHT flag is set so that this io_u
+                * can be checked by other threads as they assess overlap

                 */
                pthread_mutex_lock(&overlap_check);
                for_each_td(td, i) {
                 */
                pthread_mutex_lock(&overlap_check);
                for_each_td(td, i) {