diff mbox series

[v3,1/2] eal: add thread yield functions

Message ID 20231025163352.1076755-2-thomas@monjalon.net (mailing list archive)
State Superseded, archived
Delegated to: Thomas Monjalon
Headers
Series allow creating thread with real-time priority |

Checks

Context Check Description
ci/checkpatch success coding style OK

Commit Message

Thomas Monjalon Oct. 25, 2023, 4:31 p.m. UTC 
  When running real-time threads, we may need to force scheduling
kernel threads or other real-time threads.
New functions are added to address these cases.

The yield functions should not have any interest for normal threads.
Note: other purposes may be addressed with rte_pause() or rte_delay_*().

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
---
 lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
 lib/eal/unix/rte_thread.c    | 16 ++++++++++++++++
 lib/eal/version.map          |  4 ++++
 lib/eal/windows/rte_thread.c | 15 +++++++++++++++
 4 files changed, 57 insertions(+)

Comments

Bruce Richardson Oct. 25, 2023, 4:40 p.m. UTC | #1 
On Wed, Oct 25, 2023 at 06:31:10PM +0200, Thomas Monjalon wrote:
> When running real-time threads, we may need to force scheduling
> kernel threads or other real-time threads.
> New functions are added to address these cases.
> 
> The yield functions should not have any interest for normal threads.
> Note: other purposes may be addressed with rte_pause() or rte_delay_*().
> 
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
>  lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
>  lib/eal/unix/rte_thread.c    | 16 ++++++++++++++++
>  lib/eal/version.map          |  4 ++++
>  lib/eal/windows/rte_thread.c | 15 +++++++++++++++
>  4 files changed, 57 insertions(+)
> 
> diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
> index 8da9d4d3fb..139cafac96 100644
> --- a/lib/eal/include/rte_thread.h
> +++ b/lib/eal/include/rte_thread.h
> @@ -183,6 +183,28 @@ int rte_thread_join(rte_thread_t thread_id, uint32_t *value_ptr);
>   */
>  int rte_thread_detach(rte_thread_t thread_id);
>  
> +/**
> + * Allow another thread to run on the same CPU core.
> + *
> + * Lower priority threads may not be scheduled.
> + *
> + * Especially useful in real-time thread priority
> + * to schedule other real-time threads.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield(void);
> +
> +/**
> + * Unblock a CPU core running busy in a real-time thread.
> + *
> + * Especially useful in real-time thread priority
> + * to avoid a busy loop blocking vital threads on a core.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield_realtime(void);
> +
>  /**
>   * Get the id of the calling thread.
>   *
> diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
> index 36a21ab2f9..92b4e53adb 100644
> --- a/lib/eal/unix/rte_thread.c
> +++ b/lib/eal/unix/rte_thread.c
> @@ -5,9 +5,11 @@
>  
>  #include <errno.h>
>  #include <pthread.h>
> +#include <sched.h>
>  #include <stdbool.h>
>  #include <stdlib.h>
>  #include <string.h>
> +#include <time.h>
>  
>  #include <rte_errno.h>
>  #include <rte_log.h>
> @@ -227,6 +229,20 @@ rte_thread_detach(rte_thread_t thread_id)
>  	return pthread_detach((pthread_t)thread_id.opaque_id);
>  }
>  
> +void
> +rte_thread_yield(void)
> +{
> +	sched_yield();
> +}
> +
> +void
> +rte_thread_yield_realtime(void)
> +{
> +	/* A simple yield may not be enough to schedule kernel threads. */
> +	struct timespec wait = {.tv_nsec = 1};
> +	nanosleep(&wait, NULL);
> +}
> +
While I realise we discussed this earlier, and I also was the original
suggester of using sched_yield, I think just having just one function using
sleep is probably best after all.

/Bruce
Thomas Monjalon Oct. 25, 2023, 5:06 p.m. UTC | #2 
25/10/2023 18:40, Bruce Richardson:
> On Wed, Oct 25, 2023 at 06:31:10PM +0200, Thomas Monjalon wrote:
> > When running real-time threads, we may need to force scheduling
> > kernel threads or other real-time threads.
> > New functions are added to address these cases.
> > 
> > The yield functions should not have any interest for normal threads.
> > Note: other purposes may be addressed with rte_pause() or rte_delay_*().
> > 
> > Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> > ---
> >  lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
> >  lib/eal/unix/rte_thread.c    | 16 ++++++++++++++++
> >  lib/eal/version.map          |  4 ++++
> >  lib/eal/windows/rte_thread.c | 15 +++++++++++++++
> >  4 files changed, 57 insertions(+)
> > 
> > diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
> > index 8da9d4d3fb..139cafac96 100644
> > --- a/lib/eal/include/rte_thread.h
> > +++ b/lib/eal/include/rte_thread.h
> > @@ -183,6 +183,28 @@ int rte_thread_join(rte_thread_t thread_id, uint32_t *value_ptr);
> >   */
> >  int rte_thread_detach(rte_thread_t thread_id);
> >  
> > +/**
> > + * Allow another thread to run on the same CPU core.
> > + *
> > + * Lower priority threads may not be scheduled.
> > + *
> > + * Especially useful in real-time thread priority
> > + * to schedule other real-time threads.
> > + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> > + */
> > +__rte_experimental
> > +void rte_thread_yield(void);
> > +
> > +/**
> > + * Unblock a CPU core running busy in a real-time thread.
> > + *
> > + * Especially useful in real-time thread priority
> > + * to avoid a busy loop blocking vital threads on a core.
> > + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> > + */
> > +__rte_experimental
> > +void rte_thread_yield_realtime(void);
> > +
> >  /**
> >   * Get the id of the calling thread.
> >   *
> > diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
> > index 36a21ab2f9..92b4e53adb 100644
> > --- a/lib/eal/unix/rte_thread.c
> > +++ b/lib/eal/unix/rte_thread.c
> > @@ -5,9 +5,11 @@
> >  
> >  #include <errno.h>
> >  #include <pthread.h>
> > +#include <sched.h>
> >  #include <stdbool.h>
> >  #include <stdlib.h>
> >  #include <string.h>
> > +#include <time.h>
> >  
> >  #include <rte_errno.h>
> >  #include <rte_log.h>
> > @@ -227,6 +229,20 @@ rte_thread_detach(rte_thread_t thread_id)
> >  	return pthread_detach((pthread_t)thread_id.opaque_id);
> >  }
> >  
> > +void
> > +rte_thread_yield(void)
> > +{
> > +	sched_yield();
> > +}
> > +
> > +void
> > +rte_thread_yield_realtime(void)
> > +{
> > +	/* A simple yield may not be enough to schedule kernel threads. */
> > +	struct timespec wait = {.tv_nsec = 1};
> > +	nanosleep(&wait, NULL);
> > +}
> > +
> While I realise we discussed this earlier, and I also was the original
> suggester of using sched_yield, I think just having just one function using
> sleep is probably best after all.

I think there is a value to have a simple yield function
for scheduling between multiple real-time threads
without sleep overhead (not sure about the overhead).
If there is not much overhead, then a single function is OK.

Note I'm preparing a new version with a simple yield implemented
with the lighter SwitchToThread() on Windows.
Morten Brørup Oct. 25, 2023, 6:07 p.m. UTC | #3 
> From: Thomas Monjalon [mailto:thomas@monjalon.net]
> Sent: Wednesday, 25 October 2023 18.31
> 
> When running real-time threads, we may need to force scheduling
> kernel threads or other real-time threads.
> New functions are added to address these cases.
> 
> The yield functions should not have any interest for normal threads.
> Note: other purposes may be addressed with rte_pause() or rte_delay_*().
> 
> Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> ---
>  lib/eal/include/rte_thread.h | 22 ++++++++++++++++++++++
>  lib/eal/unix/rte_thread.c    | 16 ++++++++++++++++
>  lib/eal/version.map          |  4 ++++
>  lib/eal/windows/rte_thread.c | 15 +++++++++++++++
>  4 files changed, 57 insertions(+)
> 
> diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
> index 8da9d4d3fb..139cafac96 100644
> --- a/lib/eal/include/rte_thread.h
> +++ b/lib/eal/include/rte_thread.h
> @@ -183,6 +183,28 @@ int rte_thread_join(rte_thread_t thread_id,
> uint32_t *value_ptr);
>   */
>  int rte_thread_detach(rte_thread_t thread_id);
> 
> +/**
> + * Allow another thread to run on the same CPU core.
> + *
> + * Lower priority threads may not be scheduled.
> + *
> + * Especially useful in real-time thread priority
> + * to schedule other real-time threads.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield(void);
> +
> +/**
> + * Unblock a CPU core running busy in a real-time thread.
> + *
> + * Especially useful in real-time thread priority
> + * to avoid a busy loop blocking vital threads on a core.
> + * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
> + */
> +__rte_experimental
> +void rte_thread_yield_realtime(void);
> +

If an application really needs to use real-time priority, the behavior of any DPDK yield functions must be documented in much more detail than this - especially in regard to expected latency.

[...]

> diff --git a/lib/eal/windows/rte_thread.c b/lib/eal/windows/rte_thread.c
> index acf648456c..1e031eca40 100644
> --- a/lib/eal/windows/rte_thread.c
> +++ b/lib/eal/windows/rte_thread.c
> @@ -304,6 +304,21 @@ rte_thread_detach(rte_thread_t thread_id)
>  	return 0;
>  }
> 
> +void
> +rte_thread_yield(void)
> +{
> +	Sleep(0);
> +}
> +
> +void
> +rte_thread_yield_realtime(void)
> +{
> +	/* Real-time threads are not causing problems on Windows.
> +	 * A normal yield should be fine.

Back in the days, the Windows API had a Yield() function; make sure your comment can't be misunderstood as referring to that.

> +	 */
> +	Sleep(0);
> +}
diff mbox series

Patch

diff --git a/lib/eal/include/rte_thread.h b/lib/eal/include/rte_thread.h
index 8da9d4d3fb..139cafac96 100644
--- a/lib/eal/include/rte_thread.h
+++ b/lib/eal/include/rte_thread.h
@@ -183,6 +183,28 @@  int rte_thread_join(rte_thread_t thread_id, uint32_t *value_ptr);
  */
 int rte_thread_detach(rte_thread_t thread_id);
 
+/**
+ * Allow another thread to run on the same CPU core.
+ *
+ * Lower priority threads may not be scheduled.
+ *
+ * Especially useful in real-time thread priority
+ * to schedule other real-time threads.
+ * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
+ */
+__rte_experimental
+void rte_thread_yield(void);
+
+/**
+ * Unblock a CPU core running busy in a real-time thread.
+ *
+ * Especially useful in real-time thread priority
+ * to avoid a busy loop blocking vital threads on a core.
+ * @see RTE_THREAD_PRIORITY_REALTIME_CRITICAL
+ */
+__rte_experimental
+void rte_thread_yield_realtime(void);
+
 /**
  * Get the id of the calling thread.
  *
diff --git a/lib/eal/unix/rte_thread.c b/lib/eal/unix/rte_thread.c
index 36a21ab2f9..92b4e53adb 100644
--- a/lib/eal/unix/rte_thread.c
+++ b/lib/eal/unix/rte_thread.c
@@ -5,9 +5,11 @@ 
 
 #include <errno.h>
 #include <pthread.h>
+#include <sched.h>
 #include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include <rte_errno.h>
 #include <rte_log.h>
@@ -227,6 +229,20 @@  rte_thread_detach(rte_thread_t thread_id)
 	return pthread_detach((pthread_t)thread_id.opaque_id);
 }
 
+void
+rte_thread_yield(void)
+{
+	sched_yield();
+}
+
+void
+rte_thread_yield_realtime(void)
+{
+	/* A simple yield may not be enough to schedule kernel threads. */
+	struct timespec wait = {.tv_nsec = 1};
+	nanosleep(&wait, NULL);
+}
+
 int
 rte_thread_equal(rte_thread_t t1, rte_thread_t t2)
 {
diff --git a/lib/eal/version.map b/lib/eal/version.map
index e00a844805..b81ac3e3af 100644
--- a/lib/eal/version.map
+++ b/lib/eal/version.map
@@ -413,6 +413,10 @@  EXPERIMENTAL {
 	# added in 23.07
 	rte_memzone_max_get;
 	rte_memzone_max_set;
+
+	# added in 23.11
+	rte_thread_yield;
+	rte_thread_yield_realtime;
 };
 
 INTERNAL {
diff --git a/lib/eal/windows/rte_thread.c b/lib/eal/windows/rte_thread.c
index acf648456c..1e031eca40 100644
--- a/lib/eal/windows/rte_thread.c
+++ b/lib/eal/windows/rte_thread.c
@@ -304,6 +304,21 @@  rte_thread_detach(rte_thread_t thread_id)
 	return 0;
 }
 
+void
+rte_thread_yield(void)
+{
+	Sleep(0);
+}
+
+void
+rte_thread_yield_realtime(void)
+{
+	/* Real-time threads are not causing problems on Windows.
+	 * A normal yield should be fine.
+	 */
+	Sleep(0);
+}
+
 int
 rte_thread_equal(rte_thread_t t1, rte_thread_t t2)
 {