[dpdk-dev] 回复: [RFC 3/5] eal: lcore state FINISHED is not required

[Feifei Wang]

Hi, Honnappa

> -----Original Message-----
> From: Honnappa Nagarahalli <honnappa.nagarahalli at arm.com>
> Sent: Thursday, February 25, 2021 5:20 AM
> To: hemant.agrawal at nxp.com; Nipun.gupta at nxp.com; jerinj at marvell.com;
> Harry van Haaren <harry.van.haaren at intel.com>; Bruce Richardson
> <bruce.richardson at intel.com>; Dmitry Kozlyuk <dmitry.kozliuk at gmail.com>;
> Narcisa Ana Maria Vasile <navasile at linux.microsoft.com>; Dmitry Malloy
> <dmitrym at microsoft.com>; Pallavi Kadam <pallavi.kadam at intel.com>
> Cc: dev at dpdk.org; Honnappa Nagarahalli
> <Honnappa.Nagarahalli at arm.com>; Ruifeng Wang
> <Ruifeng.Wang at arm.com>; Feifei Wang (Arm Technology China)
> <Feifei.Wang at arm.com>; nd <nd at arm.com>
> 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

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". 

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.

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