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From: Thomas Monjalon <thomas@monjalon.net>
To: dev@dpdk.org
Cc: David Marchand <david.marchand@redhat.com>, stable@dpdk.org,
=?UTF-8?q?Morten=20Br=C3=B8rup?= <mb@smartsharesystems.com>,
Anatoly Burakov <anatoly.burakov@intel.com>,
Narcisa Vasile <navasile@linux.microsoft.com>,
Tyler Retzlaff <roretzla@linux.microsoft.com>,
Stephen Hemminger <stephen@networkplumber.org>,
Dmitry Kozlyuk <dmitry.kozliuk@gmail.com>,
Konstantin Ananyev <konstantin.v.ananyev@yandex.ru>,
Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Subject: [PATCH v5 2/2] eal/unix: allow creating thread with real-time priority
Date: Thu, 26 Oct 2023 16:19:37 +0200
Message-ID: <20231026142749.1174372-3-thomas@monjalon.net>
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<20231026142749.1174372-1-thomas@monjalon.net>
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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.
Real-time thread can block some kernel threads on the same core,
making the system unstable.
That's why a sleep is added in the test thread,
and a warning is logged when using real-time priority.
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: stable@dpdk.org
Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Morten Brørup <mb@smartsharesystems.com>
---
app/test/test_threads.c | 11 +---------
.../prog_guide/env_abstraction_layer.rst | 4 +++-
lib/eal/include/rte_thread.h | 8 +++++--
lib/eal/unix/rte_thread.c | 22 +++++++++++--------
4 files changed, 23 insertions(+), 22 deletions(-)
diff --git a/app/test/test_threads.c b/app/test/test_threads.c
index 4ac3f2671a..c14d39fc83 100644
--- a/app/test/test_threads.c
+++ b/app/test/test_threads.c
@@ -22,7 +22,7 @@ thread_main(void *arg)
__atomic_store_n(&thread_id_ready, 1, __ATOMIC_RELEASE);
while (__atomic_load_n(&thread_id_ready, __ATOMIC_ACQUIRE) == 1)
- ;
+ rte_thread_yield_realtime(); /* required for RT priority */
return 0;
}
@@ -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 f2581fe152..7ff031e1b2 100644
--- a/lib/eal/include/rte_thread.h
+++ b/lib/eal/include/rte_thread.h
@@ -56,10 +56,14 @@ typedef uint32_t (*rte_thread_func) (void *arg);
* Thread priority values.
*/
enum rte_thread_priority {
+ /** Normal thread priority, the default. */
RTE_THREAD_PRIORITY_NORMAL = 0,
- /**< normal thread priority, the default */
+ /**
+ * Highest thread priority, use with caution.
+ * WARNING: System may be unstable because of a real-time busy loop.
+ * @see rte_thread_yield_realtime().
+ */
RTE_THREAD_PRIORITY_REALTIME_CRITICAL = 1,
- /**< highest thread priority allowed */
};
/**
diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 278d8d342d..17ffb86c17 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -33,6 +33,8 @@ static int
thread_map_priority_to_os_value(enum rte_thread_priority eal_pri, int *os_pri,
int *pol)
{
+ static bool warned;
+
/* Clear the output parameters. */
*os_pri = sched_get_priority_min(SCHED_OTHER) - 1;
*pol = -1;
@@ -51,6 +53,17 @@ thread_map_priority_to_os_value(enum rte_thread_priority eal_pri, int *os_pri,
sched_get_priority_max(SCHED_OTHER)) / 2;
break;
case RTE_THREAD_PRIORITY_REALTIME_CRITICAL:
+ /*
+ * WARNING: Real-time busy loop takes priority on kernel threads,
+ * making the system unstable.
+ * There is also a known issue when using rte_ring.
+ */
+ if (!warned) {
+ RTE_LOG(NOTICE, EAL,
+ "Real-time thread is unstable if polling without sleep.\n");
+ warned = true;
+ }
+
*pol = SCHED_RR;
*os_pri = sched_get_priority_max(SCHED_RR);
break;
@@ -155,11 +168,6 @@ 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,
¶m.sched_priority, &policy);
if (ret != 0)
@@ -291,10 +299,6 @@ 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, ¶m.sched_priority,
&policy);
if (ret != 0)
--
2.42.0