[v3,1/2] eal: add thread yield functions
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Commit Message
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
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
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.
> 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);
> +}
@@ -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.
*
@@ -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)
{
@@ -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 {
@@ -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)
{