[dpdk-dev] 回复: [EXT] [PATCH v3] examples/eventdev: refactor ethdev port stop

[Feifei Wang <Feifei.Wang2@arm.com>]

> -----邮件原件-----
> 发件人: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>
> 发送时间: 2021年1月5日 18:09
> 收件人: Feifei Wang <Feifei.Wang2@arm.com>; Harry van Haaren
> <harry.van.haaren@intel.com>; Nikhil Rao <nikhil.rao@intel.com>; Pavan
> Nikhilesh <pbhagavatula@caviumnetworks.com>
> 抄送: dev@dpdk.org; jerinj@marvell.com; nd <nd@arm.com>;
> stable@dpdk.org; Ruifeng Wang <Ruifeng.Wang@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>
> 主题: RE: [EXT] [PATCH v3] examples/eventdev: refactor ethdev port stop
> 
Hi, Pavan

> Hi Feifei,
> 
> >Move eth stop code from "signal_handler" function to the end of "main"
> >function. There are two reasons for this:
> >
> >First, this improves code maintenance and makes code look simple and
> >clear. Based on this change, after receiving the interrupt signal,
> >"fdata->done" is set as 1. Then the main thread will wait all worker
> >lcores to jump out of the loop. Finally, the main thread will stop and
> >then close eth dev port.
> >
> >Second, for older version, the main thread first stops eth dev port and
> >then waits the end of worker lcore. This may cause errors because it
> >may stop the eth dev port which worker lcores are using. This moving
> >change can fix this by waiting all worker threads to exit and then stop
> >the eth dev port.
> 
> Apologies for the delayed reply,
> 
> In case of event dev the workers don't interact with eth device directly,
> Instead eth device "injects" packets into event device and event device is
> responsible for scheduling them to the workers.
> 
> If the producer is not stopped i.e. in this case eth device then the worker
> threads might never exit and the main core would wait indefinitely for
> workers to exit. This will be predominantly seen in cases where there are
> only a few flows and large number of workers causing a lot of intra thread
> dependency.

For the case that the event device scheduling packets to the workers. Though the producer
is not stopped (eth device), when the main core receive the interrupt signal, the "fdata->done"
will be set as 1. Then all the workers load the value 1 of "fdata->done" and jump out of the loop
to finish their thread.

Best Regards
Feifei
> 
> Regards,
> Pavan.
> 
> >
> >In the meanwhile, remove wmb in signal_handler.
> >
> >This is because when the main lcore receive the stop signal, it stores
> >1 into fdata->done. And then the worker lcores load "fdata->done" and
> >jump out of the loop to stop running. Nothing should be stored after
> >updating
> >fdata->done, so the wmb is unnecessary.
> >
> >Fixes: 085edac2ca38 ("examples/eventdev_pipeline: support Tx
> >adapter")
> >Cc: pbhagavatula@marvell.com
> >Cc: stable@dpdk.org
> >
> >Suggested-by: Ruifeng Wang <ruifeng.wang@arm.com>
> >Signed-off-by: Feifei Wang <feifei.wang2@arm.com>
> >Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
> >Reviewed-by: Honnappa Nagarahalli
> ><honnappa.nagarahalli@arm.com>
> >Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
> >---
> >
> >v2:
> >1. Delete unused variable to fix build error 2. Reduce commit message
> >length to fix coding style issues
> >
> >v3:
> >1. Title improvement (Van Haaren)
> >
> > examples/eventdev_pipeline/main.c | 16 ++++------------
> > 1 file changed, 4 insertions(+), 12 deletions(-)
> >
> >diff --git a/examples/eventdev_pipeline/main.c
> >b/examples/eventdev_pipeline/main.c
> >index 823f8b51c..fdbaf667b 100644
> >--- a/examples/eventdev_pipeline/main.c
> >+++ b/examples/eventdev_pipeline/main.c
> >@@ -280,7 +280,6 @@ static void
> > signal_handler(int signum)
> > {
> > 	static uint8_t once;
> >-	uint16_t portid;
> >
> > 	if (fdata->done)
> > 		rte_exit(1, "Exiting on signal %d\n", signum); @@ -291,17
> +290,6 @@
> >signal_handler(int signum)
> > 			rte_event_dev_dump(0, stdout);
> > 		once = 1;
> > 		fdata->done = 1;
> >-		rte_smp_wmb();
> >-
> >-		RTE_ETH_FOREACH_DEV(portid) {
> >-			rte_event_eth_rx_adapter_stop(portid);
> >-			rte_event_eth_tx_adapter_stop(portid);
> >-			if (rte_eth_dev_stop(portid) < 0)
> >-				printf("Failed to stop port %u", portid);
> >-		}
> >-
> >-		rte_eal_mp_wait_lcore();
> >-
> > 	}
> > 	if (signum == SIGTSTP)
> > 		rte_event_dev_dump(0, stdout);
> >@@ -465,6 +453,10 @@ main(int argc, char **argv)
> > 	}
> >
> > 	RTE_ETH_FOREACH_DEV(portid) {
> >+		rte_event_eth_rx_adapter_stop(portid);
> >+		rte_event_eth_tx_adapter_stop(portid);
> >+		if (rte_eth_dev_stop(portid) < 0)
> >+			printf("Failed to stop port %u", portid);
> > 		rte_eth_dev_close(portid);
> > 	}
> >
> >--
> >2.25.1