[PATCH] eal/unix: allow creating thread with real-time priority

[Thomas Monjalon]

When adding an API for creating threads,
the real-time priority has been forbidden on Unix.

There is a known issue with ring behaviour,
but it should not be completely forbidden.

Fixes: ca04c78b6262 ("eal: get/set thread priority per thread identifier")
Fixes: ce6e911d20f6 ("eal: add thread lifetime API")
Fixes: a7ba40b2b1bf ("drivers: convert to internal control threads")
Cc: sta...@dpdk.org

Signed-off-by: Thomas Monjalon <tho...@monjalon.net>
---
 app/test/test_threads.c                         | 9 ---------
 doc/guides/prog_guide/env_abstraction_layer.rst | 4 +++-
 lib/eal/include/rte_thread.h                    | 2 +-
 lib/eal/unix/rte_thread.c                       | 9 ---------
 4 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/app/test/test_threads.c b/app/test/test_threads.c
index 4ac3f2671a..4f7d10e074 100644
--- a/app/test/test_threads.c
+++ b/app/test/test_threads.c
@@ -97,21 +97,12 @@ test_thread_priority(void)
                "Priority set mismatches priority get");
 
        priority = RTE_THREAD_PRIORITY_REALTIME_CRITICAL;
-#ifndef RTE_EXEC_ENV_WINDOWS
-       RTE_TEST_ASSERT(rte_thread_set_priority(thread_id, priority) == ENOTSUP,
-               "Priority set to critical should fail");
-       RTE_TEST_ASSERT(rte_thread_get_priority(thread_id, &priority) == 0,
-               "Failed to get thread priority");
-       RTE_TEST_ASSERT(priority == RTE_THREAD_PRIORITY_NORMAL,
-               "Failed set to critical should have retained normal");
-#else
        RTE_TEST_ASSERT(rte_thread_set_priority(thread_id, priority) == 0,
                "Priority set to critical should succeed");
        RTE_TEST_ASSERT(rte_thread_get_priority(thread_id, &priority) == 0,
                "Failed to get thread priority");
        RTE_TEST_ASSERT(priority == RTE_THREAD_PRIORITY_REALTIME_CRITICAL,
                "Priority set mismatches priority get");
-#endif
 
        priority = RTE_THREAD_PRIORITY_NORMAL;
        RTE_TEST_ASSERT(rte_thread_set_priority(thread_id, priority) == 0,
diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst 
b/doc/guides/prog_guide/env_abstraction_layer.rst
index 6debf54efb..d1f7cae7cd 100644
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -815,7 +815,9 @@ Known Issues
 
   4. It MAY be used by preemptible multi-producer and/or preemptible 
multi-consumer pthreads whose scheduling policy are all SCHED_OTHER(cfs), 
SCHED_IDLE or SCHED_BATCH. User SHOULD be aware of the performance penalty 
before using it.
 
-  5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling 
policies are SCHED_FIFO or SCHED_RR.
+  5. It MUST not be used by multi-producer/consumer pthreads
+     whose scheduling policies are ``SCHED_FIFO``
+     or ``SCHED_RR`` (``RTE_THREAD_PRIORITY_REALTIME_CRITICAL``).
 
   Alternatively, applications can use the lock-free stack mempool handler. When
   considering this handler, note that:
diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
index 8da9d4d3fb..5e624015e4 100644
--- a/lib/eal/include/rte_thread.h
+++ b/lib/eal/include/rte_thread.h
@@ -59,7 +59,7 @@ enum rte_thread_priority {
        RTE_THREAD_PRIORITY_NORMAL            = 0,
        /**< normal thread priority, the default */
        RTE_THREAD_PRIORITY_REALTIME_CRITICAL = 1,
-       /**< highest thread priority allowed */
+       /**< highest thread priority, use with caution */
 };
 
 /**
diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 36a21ab2f9..0ff291c6f1 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -153,11 +153,6 @@ rte_thread_create(rte_thread_t *thread_id,
                        goto cleanup;
                }
 
-               if (thread_attr->priority ==
-                               RTE_THREAD_PRIORITY_REALTIME_CRITICAL) {
-                       ret = ENOTSUP;
-                       goto cleanup;
-               }
                ret = thread_map_priority_to_os_value(thread_attr->priority,
                                &param.sched_priority, &policy);
                if (ret != 0)
@@ -275,10 +270,6 @@ rte_thread_set_priority(rte_thread_t thread_id,
        int policy;
        int ret;
 
-       /* Realtime priority can cause crashes on non-Windows platforms. */
-       if (priority == RTE_THREAD_PRIORITY_REALTIME_CRITICAL)
-               return ENOTSUP;
-
        ret = thread_map_priority_to_os_value(priority, &param.sched_priority,
                &policy);
        if (ret != 0)
-- 
2.42.0