[RFC,3/5] eal: lcore state FINISHED is not required

Message ID 20210224212018.17576-4-honnappa.nagarahalli@arm.com
State New
Headers show
Series
  • Use correct memory ordering in eal functions
Related show

Commit Message

Honnappa Nagarahalli Feb. 24, 2021, 9:20 p.m.
FINISHED state seems to be used to indicate that the worker's update
of the 'state' is not visible to other threads. There seems to be no
requirement to have such a state.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>

---
 drivers/event/dpaa2/dpaa2_eventdev_selftest.c | 2 +-
 drivers/event/octeontx/ssovf_evdev_selftest.c | 2 +-
 drivers/event/sw/sw_evdev_selftest.c          | 4 ++--
 examples/l2fwd-keepalive/main.c               | 2 +-
 lib/librte_eal/common/eal_common_launch.c     | 7 ++-----
 lib/librte_eal/freebsd/eal_thread.c           | 2 +-
 lib/librte_eal/linux/eal_thread.c             | 8 +-------
 lib/librte_eal/windows/eal_thread.c           | 8 +-------
 8 files changed, 10 insertions(+), 25 deletions(-)

-- 
2.17.1

Comments

Honnappa Nagarahalli Feb. 25, 2021, 11:33 p.m. | #1
+Thomas, David, Konstantin for input

<snip>

> > Subject: [RFC 3/5] eal: lcore state FINISHED is not required

> >

> > FINISHED state seems to be used to indicate that the worker's update

> > of the 'state' is not visible to other threads. There seems to be no

> > requirement to have such a state.

> 

> I am not sure "FINISHED" is necessary to be removed, and I propose some of my

> profiles for discussion.

>  There are three states for lcore now:

> "WAIT": indicate lcore can start working

> "RUNNING": indicate lcore is working

> "FINISHED": indicate lcore has finished its working and wait to be reset

If you look at the definitions of "WAIT" and "FINISHED" states, they look similar, except for "wait to be reset" in "FINISHED" state . The code really does not do anything to reset the lcore. It just changes the state to "WAIT".

> 

> From the description above, we can find "FINISHED" is different from "WAIT", it

> can shows that lcore has done the work and finished it. Thus, if we remove

> "FINISHED", maybe we will not know whether the lcore finishes its work or just

> doesn't start, because this two state has the same tag "WAIT".

Looking at "eal_thread_loop", the worker thread sets the state to "RUNNING" before sending the ack back to main core. After that it is guaranteed that the worker will run the assigned function. Only case where it will not run the assigned function is when the 'write' syscall fails, in which case it results in a panic.

> 

> Furthermore, consider such a scenario:

> Core 1 need to monitor Core 2 state, if Core 2 finishes one task, Core 1 can start

> its working.

> However, if there is only  one tag "WAIT", Core 1 maybe  start its work at the

> wrong time, when Core 2 still does not start its task at state "WAIT".

> This is just my guess, and at present, there is no similar application scenario in

> dpdk.

To be able to do this effectively, core 1 needs to observe the state change from WAIT->RUNNING->FINISHED. This requires that core 1 should be calling rte_eal_remote_launch and rte_eal_wait_lcore functions. It is not possible to observe this state transition from a 3rd core (for ex: a worker might go from RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be able to observe).

> 

> On the other hand, if we decide to remove "FINISHED", please consider the

> following files:

> 1. lib/librte_eal/linux/eal_thread.c: line 31

>     lib/librte_eal/windows/eal_thread.c: line 22

>     lib/librte_eal/freebsd/eal_thread.c: line 31

I have looked at these lines, they do not capture "why" FINISHED state is required.

 2.
> lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3. examples/l2fwd-

> keepalive/main.c: line 510

> rte_eal_wait_lcore(id_core) can be removed. Because the core state has been

> checked as "WAIT", this is a redundant operation

> 

> Best Regards

> Feifei

> 

> >

> > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>

> > Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>

> > ---

> >  drivers/event/dpaa2/dpaa2_eventdev_selftest.c | 2 +-

> > drivers/event/octeontx/ssovf_evdev_selftest.c | 2 +-

> >  drivers/event/sw/sw_evdev_selftest.c          | 4 ++--

> >  examples/l2fwd-keepalive/main.c               | 2 +-

> >  lib/librte_eal/common/eal_common_launch.c     | 7 ++-----

> >  lib/librte_eal/freebsd/eal_thread.c           | 2 +-

> >  lib/librte_eal/linux/eal_thread.c             | 8 +-------

> >  lib/librte_eal/windows/eal_thread.c           | 8 +-------

> >  8 files changed, 10 insertions(+), 25 deletions(-)

> >

> > diff --git a/drivers/event/dpaa2/dpaa2_eventdev_selftest.c

> > b/drivers/event/dpaa2/dpaa2_eventdev_selftest.c

> > index cd7311a94..bbbd20951 100644

> > --- a/drivers/event/dpaa2/dpaa2_eventdev_selftest.c

> > +++ b/drivers/event/dpaa2/dpaa2_eventdev_selftest.c

> > @@ -468,7 +468,7 @@ wait_workers_to_join(int lcore, const

> > rte_atomic32_t

> > *count)  RTE_SET_USED(count);

> >

> >  print_cycles = cycles = rte_get_timer_cycles(); -while

> > (rte_eal_get_lcore_state(lcore) != FINISHED) {

> > +while (rte_eal_get_lcore_state(lcore) != WAIT) {

> >  uint64_t new_cycles = rte_get_timer_cycles();

> >

> >  if (new_cycles - print_cycles > rte_get_timer_hz()) { diff --git

> > a/drivers/event/octeontx/ssovf_evdev_selftest.c

> > b/drivers/event/octeontx/ssovf_evdev_selftest.c

> > index 528f99dd8..d7b0d2211 100644

> > --- a/drivers/event/octeontx/ssovf_evdev_selftest.c

> > +++ b/drivers/event/octeontx/ssovf_evdev_selftest.c

> > @@ -579,7 +579,7 @@ wait_workers_to_join(int lcore, const

> > rte_atomic32_t

> > *count)  RTE_SET_USED(count);

> >

> >  print_cycles = cycles = rte_get_timer_cycles(); -while

> > (rte_eal_get_lcore_state(lcore) != FINISHED) {

> > +while (rte_eal_get_lcore_state(lcore) != WAIT) {

> >  uint64_t new_cycles = rte_get_timer_cycles();

> >

> >  if (new_cycles - print_cycles > rte_get_timer_hz()) { diff --git

> > a/drivers/event/sw/sw_evdev_selftest.c

> > b/drivers/event/sw/sw_evdev_selftest.c

> > index e4bfb3a0f..7847a8645 100644

> > --- a/drivers/event/sw/sw_evdev_selftest.c

> > +++ b/drivers/event/sw/sw_evdev_selftest.c

> > @@ -3138,8 +3138,8 @@ worker_loopback(struct test *t, uint8_t

> > disable_implicit_release)

> > rte_eal_remote_launch(worker_loopback_worker_fn, t, w_lcore);

> >

> >  print_cycles = cycles = rte_get_timer_cycles(); -while

> > (rte_eal_get_lcore_state(p_lcore) != FINISHED ||

> > -rte_eal_get_lcore_state(w_lcore) != FINISHED) {

> > +while (rte_eal_get_lcore_state(p_lcore) != WAIT ||

> > +rte_eal_get_lcore_state(w_lcore) != WAIT) {

> >

> >  rte_service_run_iter_on_app_lcore(t->service_id, 1);

> >

> > diff --git a/examples/l2fwd-keepalive/main.c b/examples/l2fwd-

> > keepalive/main.c index e4c2b2793..dd777c46a 100644

> > --- a/examples/l2fwd-keepalive/main.c

> > +++ b/examples/l2fwd-keepalive/main.c

> > @@ -506,7 +506,7 @@ dead_core(__rte_unused void *ptr_data, const int

> > id_core)  if (terminate_signal_received)  return;  printf("Dead core

> > %i - restarting..\n", id_core); -if (rte_eal_get_lcore_state(id_core)

> > == FINISHED) {

> > +if (rte_eal_get_lcore_state(id_core) == WAIT) {

> >  rte_eal_wait_lcore(id_core);

> >  rte_eal_remote_launch(l2fwd_launch_one_lcore, NULL, id_core);  } else

> > { diff --git a/lib/librte_eal/common/eal_common_launch.c

> > b/lib/librte_eal/common/eal_common_launch.c

> > index 34f854ad8..78fd94026 100644

> > --- a/lib/librte_eal/common/eal_common_launch.c

> > +++ b/lib/librte_eal/common/eal_common_launch.c

> > @@ -26,14 +26,11 @@ rte_eal_wait_lcore(unsigned worker_id)  if

> > (lcore_config[worker_id].state == WAIT)  return 0;

> >

> > -while (lcore_config[worker_id].state != WAIT &&

> > -       lcore_config[worker_id].state != FINISHED)

> > +while (lcore_config[worker_id].state != WAIT)

> >  rte_pause();

> >

> >  rte_rmb();

> >

> > -/* we are in finished state, go to wait state */ -

> > lcore_config[worker_id].state = WAIT;  return

> > lcore_config[worker_id].ret;  }

> >

> > @@ -62,7 +59,7 @@ rte_eal_mp_remote_launch(int (*f)(void *), void

> > *arg,

> >

> >  if (call_main == CALL_MAIN) {

> >  lcore_config[main_lcore].ret = f(arg);

> > -lcore_config[main_lcore].state = FINISHED;

> > +lcore_config[main_lcore].state = WAIT;

> >  }

> >

> >  return 0;

> > diff --git a/lib/librte_eal/freebsd/eal_thread.c

> > b/lib/librte_eal/freebsd/eal_thread.c

> > index 17b8f3996..6d6f1e2fd 100644

> > --- a/lib/librte_eal/freebsd/eal_thread.c

> > +++ b/lib/librte_eal/freebsd/eal_thread.c

> > @@ -140,7 +140,7 @@ eal_thread_loop(__rte_unused void *arg)

> > lcore_config[lcore_id].f = NULL;  lcore_config[lcore_id].arg = NULL;

> > rte_wmb(); -lcore_config[lcore_id].state = FINISHED;

> > +lcore_config[lcore_id].state = WAIT;

> >  }

> >

> >  /* never reached */

> > diff --git a/lib/librte_eal/linux/eal_thread.c

> > b/lib/librte_eal/linux/eal_thread.c

> > index a0a009104..7b9463df3 100644

> > --- a/lib/librte_eal/linux/eal_thread.c

> > +++ b/lib/librte_eal/linux/eal_thread.c

> > @@ -141,13 +141,7 @@ eal_thread_loop(__rte_unused void *arg)

> > lcore_config[lcore_id].arg = NULL;  rte_wmb();

> >

> > -/* when a service core returns, it should go directly to WAIT

> > - * state, because the application will not lcore_wait() for it.

> > - */

> > -if (lcore_config[lcore_id].core_role == ROLE_SERVICE) -

> > lcore_config[lcore_id].state = WAIT; -else

> > -lcore_config[lcore_id].state = FINISHED;

> > +lcore_config[lcore_id].state = WAIT;

> >  }

> >

> >  /* never reached */

> > diff --git a/lib/librte_eal/windows/eal_thread.c

> > b/lib/librte_eal/windows/eal_thread.c

> > index 7a9277c51..35d059a30 100644

> > --- a/lib/librte_eal/windows/eal_thread.c

> > +++ b/lib/librte_eal/windows/eal_thread.c

> > @@ -125,13 +125,7 @@ eal_thread_loop(void *arg __rte_unused)

> > lcore_config[lcore_id].arg = NULL;  rte_wmb();

> >

> > -/* when a service core returns, it should go directly to WAIT

> > - * state, because the application will not lcore_wait() for it.

> > - */

> > -if (lcore_config[lcore_id].core_role == ROLE_SERVICE) -

> > lcore_config[lcore_id].state = WAIT; -else

> > -lcore_config[lcore_id].state = FINISHED;

> > +lcore_config[lcore_id].state = WAIT;

> >  }

> >  }

> >

> > --

> > 2.17.1

> >
Thomas Monjalon Feb. 26, 2021, 8:26 a.m. | #2
26/02/2021 00:33, Honnappa Nagarahalli:
> +Thomas, David, Konstantin for input

> 

> <snip>

> 

> > > Subject: [RFC 3/5] eal: lcore state FINISHED is not required

> > >

> > > FINISHED state seems to be used to indicate that the worker's update

> > > of the 'state' is not visible to other threads. There seems to be no

> > > requirement to have such a state.

> > 

> > I am not sure "FINISHED" is necessary to be removed, and I propose some of my

> > profiles for discussion.

> >  There are three states for lcore now:

> > "WAIT": indicate lcore can start working

> > "RUNNING": indicate lcore is working

> > "FINISHED": indicate lcore has finished its working and wait to be reset

> If you look at the definitions of "WAIT" and "FINISHED" states, they look similar, except for "wait to be reset" in "FINISHED" state . The code really does not do anything to reset the lcore. It just changes the state to "WAIT".

> 

> > 

> > From the description above, we can find "FINISHED" is different from "WAIT", it

> > can shows that lcore has done the work and finished it. Thus, if we remove

> > "FINISHED", maybe we will not know whether the lcore finishes its work or just

> > doesn't start, because this two state has the same tag "WAIT".

> Looking at "eal_thread_loop", the worker thread sets the state to "RUNNING" before sending the ack back to main core. After that it is guaranteed that the worker will run the assigned function. Only case where it will not run the assigned function is when the 'write' syscall fails, in which case it results in a panic.


Quick note: it should not panic.
We must find a way to return an error
without crashing the whole application.

 
> > Furthermore, consider such a scenario:

> > Core 1 need to monitor Core 2 state, if Core 2 finishes one task, Core 1 can start

> > its working.

> > However, if there is only  one tag "WAIT", Core 1 maybe  start its work at the

> > wrong time, when Core 2 still does not start its task at state "WAIT".

> > This is just my guess, and at present, there is no similar application scenario in

> > dpdk.

> To be able to do this effectively, core 1 needs to observe the state change from WAIT->RUNNING->FINISHED. This requires that core 1 should be calling rte_eal_remote_launch and rte_eal_wait_lcore functions. It is not possible to observe this state transition from a 3rd core (for ex: a worker might go from RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be able to observe).

> 

> > 

> > On the other hand, if we decide to remove "FINISHED", please consider the

> > following files:

> > 1. lib/librte_eal/linux/eal_thread.c: line 31

> >     lib/librte_eal/windows/eal_thread.c: line 22

> >     lib/librte_eal/freebsd/eal_thread.c: line 31

> I have looked at these lines, they do not capture "why" FINISHED state is required.

> 

>  2.

> > lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3. examples/l2fwd-

> > keepalive/main.c: line 510

> > rte_eal_wait_lcore(id_core) can be removed. Because the core state has been

> > checked as "WAIT", this is a redundant operation
Honnappa Nagarahalli March 2, 2021, 3:13 a.m. | #3
<snip>

> >

> > > > Subject: [RFC 3/5] eal: lcore state FINISHED is not required

> > > >

> > > > FINISHED state seems to be used to indicate that the worker's

> > > > update of the 'state' is not visible to other threads. There seems

> > > > to be no requirement to have such a state.

> > >

> > > I am not sure "FINISHED" is necessary to be removed, and I propose

> > > some of my profiles for discussion.

> > >  There are three states for lcore now:

> > > "WAIT": indicate lcore can start working

> > > "RUNNING": indicate lcore is working

> > > "FINISHED": indicate lcore has finished its working and wait to be

> > > reset

> > If you look at the definitions of "WAIT" and "FINISHED" states, they look

> similar, except for "wait to be reset" in "FINISHED" state . The code really does

> not do anything to reset the lcore. It just changes the state to "WAIT".

> >

> > >

> > > From the description above, we can find "FINISHED" is different from

> > > "WAIT", it can shows that lcore has done the work and finished it.

> > > Thus, if we remove "FINISHED", maybe we will not know whether the

> > > lcore finishes its work or just doesn't start, because this two state has the

> same tag "WAIT".

> > Looking at "eal_thread_loop", the worker thread sets the state to "RUNNING"

> before sending the ack back to main core. After that it is guaranteed that the

> worker will run the assigned function. Only case where it will not run the

> assigned function is when the 'write' syscall fails, in which case it results in a

> panic.

> 

> Quick note: it should not panic.

> We must find a way to return an error

> without crashing the whole application.

The syscalls are being used to communicate the status back to the main thread. If they fail, it is not possible to communicate the status. May be it is better to panic.
We could change the implementation using shared variables, but it would require polling the memory. May be the syscalls are being used to avoid polling. However, this polling would happen during init time (or similar) for a short duration.

> 

> 

> > > Furthermore, consider such a scenario:

> > > Core 1 need to monitor Core 2 state, if Core 2 finishes one task,

> > > Core 1 can start its working.

> > > However, if there is only  one tag "WAIT", Core 1 maybe  start its

> > > work at the wrong time, when Core 2 still does not start its task at state

> "WAIT".

> > > This is just my guess, and at present, there is no similar

> > > application scenario in dpdk.

> > To be able to do this effectively, core 1 needs to observe the state change

> from WAIT->RUNNING->FINISHED. This requires that core 1 should be calling

> rte_eal_remote_launch and rte_eal_wait_lcore functions. It is not possible to

> observe this state transition from a 3rd core (for ex: a worker might go from

> RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be able to

> observe).

> >

> > >

> > > On the other hand, if we decide to remove "FINISHED", please

> > > consider the following files:

> > > 1. lib/librte_eal/linux/eal_thread.c: line 31

> > >     lib/librte_eal/windows/eal_thread.c: line 22

> > >     lib/librte_eal/freebsd/eal_thread.c: line 31

> > I have looked at these lines, they do not capture "why" FINISHED state is

> required.

> >

> >  2.

> > > lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3.

> > > examples/l2fwd-

> > > keepalive/main.c: line 510

> > > rte_eal_wait_lcore(id_core) can be removed. Because the core state

> > > has been checked as "WAIT", this is a redundant operation

> 

>
Ananyev, Konstantin March 19, 2021, 1:42 p.m. | #4
Hi everyone,

> <snip>

> 

> > >

> > > > > Subject: [RFC 3/5] eal: lcore state FINISHED is not required

> > > > >

> > > > > FINISHED state seems to be used to indicate that the worker's

> > > > > update of the 'state' is not visible to other threads. There seems

> > > > > to be no requirement to have such a state.

> > > >

> > > > I am not sure "FINISHED" is necessary to be removed, and I propose

> > > > some of my profiles for discussion.

> > > >  There are three states for lcore now:

> > > > "WAIT": indicate lcore can start working

> > > > "RUNNING": indicate lcore is working

> > > > "FINISHED": indicate lcore has finished its working and wait to be

> > > > reset

> > > If you look at the definitions of "WAIT" and "FINISHED" states, they look

> > similar, except for "wait to be reset" in "FINISHED" state . The code really does

> > not do anything to reset the lcore. It just changes the state to "WAIT".



I agree that 3 states here seems excessive.
Just 2 (RUNNING/IDLE) seems enough.
Though we can't just remove FINISHED here - it will be an Abi breakage.
Might be deprecate FINISHED now and remove in 21.11.

Also need to decide what rte_eal_wait_lcore() should return in that case?
Always zero, or always status of last function called?

> > >

> > > >

> > > > From the description above, we can find "FINISHED" is different from

> > > > "WAIT", it can shows that lcore has done the work and finished it.

> > > > Thus, if we remove "FINISHED", maybe we will not know whether the

> > > > lcore finishes its work or just doesn't start, because this two state has the

> > same tag "WAIT".

> > > Looking at "eal_thread_loop", the worker thread sets the state to "RUNNING"

> > before sending the ack back to main core. After that it is guaranteed that the

> > worker will run the assigned function. Only case where it will not run the

> > assigned function is when the 'write' syscall fails, in which case it results in a

> > panic.

> >

> > Quick note: it should not panic.

> > We must find a way to return an error

> > without crashing the whole application.

> The syscalls are being used to communicate the status back to the main thread. If they fail, it is not possible to communicate the status.

> May be it is better to panic.

> We could change the implementation using shared variables, but it would require polling the memory. May be the syscalls are being used to

> avoid polling. However, this polling would happen during init time (or similar) for a short duration.


AFAIK we use read and write not for status communication, but sort of sleep/ack point.
Though I agree if we can't do read/write from the system pipe then something is totally wrong,
and probably there is no much point to continue. 
 
> >

> >

> > > > Furthermore, consider such a scenario:

> > > > Core 1 need to monitor Core 2 state, if Core 2 finishes one task,

> > > > Core 1 can start its working.

> > > > However, if there is only  one tag "WAIT", Core 1 maybe  start its

> > > > work at the wrong time, when Core 2 still does not start its task at state

> > "WAIT".

> > > > This is just my guess, and at present, there is no similar

> > > > application scenario in dpdk.

> > > To be able to do this effectively, core 1 needs to observe the state change

> > from WAIT->RUNNING->FINISHED. This requires that core 1 should be calling

> > rte_eal_remote_launch and rte_eal_wait_lcore functions. It is not possible to

> > observe this state transition from a 3rd core (for ex: a worker might go from

> > RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be able to

> > observe).

> > >

> > > >

> > > > On the other hand, if we decide to remove "FINISHED", please

> > > > consider the following files:

> > > > 1. lib/librte_eal/linux/eal_thread.c: line 31

> > > >     lib/librte_eal/windows/eal_thread.c: line 22

> > > >     lib/librte_eal/freebsd/eal_thread.c: line 31

> > > I have looked at these lines, they do not capture "why" FINISHED state is

> > required.

> > >

> > >  2.

> > > > lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3.

> > > > examples/l2fwd-

> > > > keepalive/main.c: line 510

> > > > rte_eal_wait_lcore(id_core) can be removed. Because the core state

> > > > has been checked as "WAIT", this is a redundant operation

> >

> >
Honnappa Nagarahalli March 30, 2021, 2:54 a.m. | #5
<snip>

> 

> Hi everyone,

Thanks Konstantin for the review.

> 

> > <snip>

> >

> > > >

> > > > > > Subject: [RFC 3/5] eal: lcore state FINISHED is not required

> > > > > >

> > > > > > FINISHED state seems to be used to indicate that the worker's

> > > > > > update of the 'state' is not visible to other threads. There

> > > > > > seems to be no requirement to have such a state.

> > > > >

> > > > > I am not sure "FINISHED" is necessary to be removed, and I

> > > > > propose some of my profiles for discussion.

> > > > >  There are three states for lcore now:

> > > > > "WAIT": indicate lcore can start working

> > > > > "RUNNING": indicate lcore is working

> > > > > "FINISHED": indicate lcore has finished its working and wait to

> > > > > be reset

> > > > If you look at the definitions of "WAIT" and "FINISHED" states,

> > > > they look

> > > similar, except for "wait to be reset" in "FINISHED" state . The

> > > code really does not do anything to reset the lcore. It just changes the

> state to "WAIT".

> 

> 

> I agree that 3 states here seems excessive.

> Just 2 (RUNNING/IDLE) seems enough.

> Though we can't just remove FINISHED here - it will be an Abi breakage.

> Might be deprecate FINISHED now and remove in 21.11.

Agree, will add a new patch to deprecate the FINISHED state. Also, does the deprecation notice need to go into 20.08 release notes?

> 

> Also need to decide what rte_eal_wait_lcore() should return in that case?

> Always zero, or always status of last function called?

I am not sure why ' rte_eal_wait_lcore' has the following code:

if (lcore_config[worker_id].state == WAIT)
                return 0;

This indicates that the caller has called 'rte_eal_wait_lcore' function earlier. May be there is a use case where there are multiple threads waiting for the lcores to complete?
Anyway, IMO, returning the status of the last function always is better for this API.

> 

> > > >

> > > > >

> > > > > From the description above, we can find "FINISHED" is different

> > > > > from "WAIT", it can shows that lcore has done the work and finished

> it.

> > > > > Thus, if we remove "FINISHED", maybe we will not know whether

> > > > > the lcore finishes its work or just doesn't start, because this

> > > > > two state has the

> > > same tag "WAIT".

> > > > Looking at "eal_thread_loop", the worker thread sets the state to

> "RUNNING"

> > > before sending the ack back to main core. After that it is

> > > guaranteed that the worker will run the assigned function. Only case

> > > where it will not run the assigned function is when the 'write'

> > > syscall fails, in which case it results in a panic.

> > >

> > > Quick note: it should not panic.

> > > We must find a way to return an error without crashing the whole

> > > application.

> > The syscalls are being used to communicate the status back to the main

> thread. If they fail, it is not possible to communicate the status.

> > May be it is better to panic.

> > We could change the implementation using shared variables, but it

> > would require polling the memory. May be the syscalls are being used to

> avoid polling. However, this polling would happen during init time (or similar)

> for a short duration.

> 

> AFAIK we use read and write not for status communication, but sort of

> sleep/ack point.

> Though I agree if we can't do read/write from the system pipe then

> something is totally wrong, and probably there is no much point to continue.

> 

> > >

> > >

> > > > > Furthermore, consider such a scenario:

> > > > > Core 1 need to monitor Core 2 state, if Core 2 finishes one

> > > > > task, Core 1 can start its working.

> > > > > However, if there is only  one tag "WAIT", Core 1 maybe  start

> > > > > its work at the wrong time, when Core 2 still does not start its

> > > > > task at state

> > > "WAIT".

> > > > > This is just my guess, and at present, there is no similar

> > > > > application scenario in dpdk.

> > > > To be able to do this effectively, core 1 needs to observe the

> > > > state change

> > > from WAIT->RUNNING->FINISHED. This requires that core 1 should be

> > > calling rte_eal_remote_launch and rte_eal_wait_lcore functions. It

> > > is not possible to observe this state transition from a 3rd core

> > > (for ex: a worker might go from

> > > RUNNING->FINISHED->WAIT->RUNNING which a 3rd core might not be

> able

> > > RUNNING->FINISHED->WAIT->to

> > > observe).

> > > >

> > > > >

> > > > > On the other hand, if we decide to remove "FINISHED", please

> > > > > consider the following files:

> > > > > 1. lib/librte_eal/linux/eal_thread.c: line 31

> > > > >     lib/librte_eal/windows/eal_thread.c: line 22

> > > > >     lib/librte_eal/freebsd/eal_thread.c: line 31

> > > > I have looked at these lines, they do not capture "why" FINISHED

> > > > state is

> > > required.

> > > >

> > > >  2.

> > > > > lib/librte_eal/include/rte_launch.h: line 24, 44, 121, 123, 131 3.

> > > > > examples/l2fwd-

> > > > > keepalive/main.c: line 510

> > > > > rte_eal_wait_lcore(id_core) can be removed. Because the core

> > > > > state has been checked as "WAIT", this is a redundant operation

> > >

> > >

Patch

diff --git a/drivers/event/dpaa2/dpaa2_eventdev_selftest.c b/drivers/event/dpaa2/dpaa2_eventdev_selftest.c
index cd7311a94..bbbd20951 100644
--- a/drivers/event/dpaa2/dpaa2_eventdev_selftest.c
+++ b/drivers/event/dpaa2/dpaa2_eventdev_selftest.c
@@ -468,7 +468,7 @@  wait_workers_to_join(int lcore, const rte_atomic32_t *count)
 	RTE_SET_USED(count);
 
 	print_cycles = cycles = rte_get_timer_cycles();
-	while (rte_eal_get_lcore_state(lcore) != FINISHED) {
+	while (rte_eal_get_lcore_state(lcore) != WAIT) {
 		uint64_t new_cycles = rte_get_timer_cycles();
 
 		if (new_cycles - print_cycles > rte_get_timer_hz()) {
diff --git a/drivers/event/octeontx/ssovf_evdev_selftest.c b/drivers/event/octeontx/ssovf_evdev_selftest.c
index 528f99dd8..d7b0d2211 100644
--- a/drivers/event/octeontx/ssovf_evdev_selftest.c
+++ b/drivers/event/octeontx/ssovf_evdev_selftest.c
@@ -579,7 +579,7 @@  wait_workers_to_join(int lcore, const rte_atomic32_t *count)
 	RTE_SET_USED(count);
 
 	print_cycles = cycles = rte_get_timer_cycles();
-	while (rte_eal_get_lcore_state(lcore) != FINISHED) {
+	while (rte_eal_get_lcore_state(lcore) != WAIT) {
 		uint64_t new_cycles = rte_get_timer_cycles();
 
 		if (new_cycles - print_cycles > rte_get_timer_hz()) {
diff --git a/drivers/event/sw/sw_evdev_selftest.c b/drivers/event/sw/sw_evdev_selftest.c
index e4bfb3a0f..7847a8645 100644
--- a/drivers/event/sw/sw_evdev_selftest.c
+++ b/drivers/event/sw/sw_evdev_selftest.c
@@ -3138,8 +3138,8 @@  worker_loopback(struct test *t, uint8_t disable_implicit_release)
 	rte_eal_remote_launch(worker_loopback_worker_fn, t, w_lcore);
 
 	print_cycles = cycles = rte_get_timer_cycles();
-	while (rte_eal_get_lcore_state(p_lcore) != FINISHED ||
-			rte_eal_get_lcore_state(w_lcore) != FINISHED) {
+	while (rte_eal_get_lcore_state(p_lcore) != WAIT ||
+			rte_eal_get_lcore_state(w_lcore) != WAIT) {
 
 		rte_service_run_iter_on_app_lcore(t->service_id, 1);
 
diff --git a/examples/l2fwd-keepalive/main.c b/examples/l2fwd-keepalive/main.c
index e4c2b2793..dd777c46a 100644
--- a/examples/l2fwd-keepalive/main.c
+++ b/examples/l2fwd-keepalive/main.c
@@ -506,7 +506,7 @@  dead_core(__rte_unused void *ptr_data, const int id_core)
 	if (terminate_signal_received)
 		return;
 	printf("Dead core %i - restarting..\n", id_core);
-	if (rte_eal_get_lcore_state(id_core) == FINISHED) {
+	if (rte_eal_get_lcore_state(id_core) == WAIT) {
 		rte_eal_wait_lcore(id_core);
 		rte_eal_remote_launch(l2fwd_launch_one_lcore, NULL, id_core);
 	} else {
diff --git a/lib/librte_eal/common/eal_common_launch.c b/lib/librte_eal/common/eal_common_launch.c
index 34f854ad8..78fd94026 100644
--- a/lib/librte_eal/common/eal_common_launch.c
+++ b/lib/librte_eal/common/eal_common_launch.c
@@ -26,14 +26,11 @@  rte_eal_wait_lcore(unsigned worker_id)
 	if (lcore_config[worker_id].state == WAIT)
 		return 0;
 
-	while (lcore_config[worker_id].state != WAIT &&
-	       lcore_config[worker_id].state != FINISHED)
+	while (lcore_config[worker_id].state != WAIT)
 		rte_pause();
 
 	rte_rmb();
 
-	/* we are in finished state, go to wait state */
-	lcore_config[worker_id].state = WAIT;
 	return lcore_config[worker_id].ret;
 }
 
@@ -62,7 +59,7 @@  rte_eal_mp_remote_launch(int (*f)(void *), void *arg,
 
 	if (call_main == CALL_MAIN) {
 		lcore_config[main_lcore].ret = f(arg);
-		lcore_config[main_lcore].state = FINISHED;
+		lcore_config[main_lcore].state = WAIT;
 	}
 
 	return 0;
diff --git a/lib/librte_eal/freebsd/eal_thread.c b/lib/librte_eal/freebsd/eal_thread.c
index 17b8f3996..6d6f1e2fd 100644
--- a/lib/librte_eal/freebsd/eal_thread.c
+++ b/lib/librte_eal/freebsd/eal_thread.c
@@ -140,7 +140,7 @@  eal_thread_loop(__rte_unused void *arg)
 		lcore_config[lcore_id].f = NULL;
 		lcore_config[lcore_id].arg = NULL;
 		rte_wmb();
-		lcore_config[lcore_id].state = FINISHED;
+		lcore_config[lcore_id].state = WAIT;
 	}
 
 	/* never reached */
diff --git a/lib/librte_eal/linux/eal_thread.c b/lib/librte_eal/linux/eal_thread.c
index a0a009104..7b9463df3 100644
--- a/lib/librte_eal/linux/eal_thread.c
+++ b/lib/librte_eal/linux/eal_thread.c
@@ -141,13 +141,7 @@  eal_thread_loop(__rte_unused void *arg)
 		lcore_config[lcore_id].arg = NULL;
 		rte_wmb();
 
-		/* when a service core returns, it should go directly to WAIT
-		 * state, because the application will not lcore_wait() for it.
-		 */
-		if (lcore_config[lcore_id].core_role == ROLE_SERVICE)
-			lcore_config[lcore_id].state = WAIT;
-		else
-			lcore_config[lcore_id].state = FINISHED;
+		lcore_config[lcore_id].state = WAIT;
 	}
 
 	/* never reached */
diff --git a/lib/librte_eal/windows/eal_thread.c b/lib/librte_eal/windows/eal_thread.c
index 7a9277c51..35d059a30 100644
--- a/lib/librte_eal/windows/eal_thread.c
+++ b/lib/librte_eal/windows/eal_thread.c
@@ -125,13 +125,7 @@  eal_thread_loop(void *arg __rte_unused)
 		lcore_config[lcore_id].arg = NULL;
 		rte_wmb();
 
-		/* when a service core returns, it should go directly to WAIT
-		 * state, because the application will not lcore_wait() for it.
-		 */
-		if (lcore_config[lcore_id].core_role == ROLE_SERVICE)
-			lcore_config[lcore_id].state = WAIT;
-		else
-			lcore_config[lcore_id].state = FINISHED;
+		lcore_config[lcore_id].state = WAIT;
 	}
 }