Re: [dpdk-dev] [PATCH] eal/interrupts: add function to allow interruptible epoll

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

Hi Stephen,
	Looks good overall, few nits inline.

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Stephen Hemminger
> Sent: Wednesday, July 24, 2019 12:21 PM
> To: dev@dpdk.org
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Subject: [dpdk-dev] [PATCH] eal/interrupts: add function to allow
> interruptible epoll
> 
> The existing definition of rte_epoll_wait retries if interrupted by a signal.
> This behavior makes it hard to use rte_epoll_wait for applications that want
> to use signals do do things like exit polling loop and shutdown.
nit                        ^^ to

> 
> Since changing existing semantic might break applications, add a new
> rte_epoll_wait_interruptible() function that does the same thing as
> rte_epoll_wait but will return -1 and errno of EINTR if it receives a signal.
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
>  .../common/include/rte_eal_interrupts.h       | 23 +++++++++
>  lib/librte_eal/freebsd/eal/eal_interrupts.c   | 12 +++++
>  lib/librte_eal/linux/eal/eal_interrupts.c     | 47 ++++++++++++-------
>  lib/librte_eal/rte_eal_version.map            |  1 +
Can you rebase with the master? It will help me apply this cleanly.

>  4 files changed, 65 insertions(+), 18 deletions(-)
> 
> diff --git a/lib/librte_eal/common/include/rte_eal_interrupts.h
> b/lib/librte_eal/common/include/rte_eal_interrupts.h
> index b370c0d26458..ac1c830f37a1 100644
> --- a/lib/librte_eal/common/include/rte_eal_interrupts.h
> +++ b/lib/librte_eal/common/include/rte_eal_interrupts.h
> @@ -87,6 +87,7 @@ struct rte_intr_handle {
> 
>  /**
>   * It waits for events on the epoll instance.
> + * Retries if signal received.
>   *
>   * @param epfd
>   *   Epoll instance fd on which the caller wait for events.
> @@ -105,6 +106,28 @@ int
>  rte_epoll_wait(int epfd, struct rte_epoll_event *events,
>  	       int maxevents, int timeout);
> 
> +/**
> + * It waits for events on the epoll instance.
> + * Does not retry if signal received.
> + *
> + * @param epfd
> + *   Epoll instance fd on which the caller wait for events.
> + * @param events
> + *   Memory area contains the events that will be available for the caller.
> + * @param maxevents
> + *   Up to maxevents are returned, must greater than zero.
> + * @param timeout
It would be good to mention the units here, but might add complexities depending on the functionality supported by the underlying OS.

> + *   Specifying a timeout of -1 causes a block indefinitely.
> + *   Specifying a timeout equal to zero cause to return immediately.
> + * @return
> + *   - On success, returns the number of available event.
> + *   - On failure, a negative value.
> + */
> +__rte_experimental
> +int
> +rte_epoll_wait_interruptible(int epfd, struct rte_epoll_event *events,
> +	       int maxevents, int timeout);
> +
>  /**
>   * It performs control operations on epoll instance referred by the epfd.
>   * It requests that the operation op be performed for the target fd.
> diff --git a/lib/librte_eal/freebsd/eal/eal_interrupts.c
> b/lib/librte_eal/freebsd/eal/eal_interrupts.c
> index f6831b7902c5..d3f8fd78a1ee 100644
> --- a/lib/librte_eal/freebsd/eal/eal_interrupts.c
> +++ b/lib/librte_eal/freebsd/eal/eal_interrupts.c
> @@ -649,6 +649,18 @@ rte_epoll_wait(int epfd, struct rte_epoll_event
> *events,
>  	return -ENOTSUP;
>  }
> 
> +int
> +rte_epoll_wait_interruptible(int epfd, struct rte_epoll_event *events,
> +			     int maxevents, int timeout)
> +{
> +	RTE_SET_USED(epfd);
> +	RTE_SET_USED(events);
> +	RTE_SET_USED(maxevents);
> +	RTE_SET_USED(timeout);
> +
> +	return -ENOTSUP;
> +}
> +
>  int
>  rte_epoll_ctl(int epfd, int op, int fd, struct rte_epoll_event *event)  { diff --
> git a/lib/librte_eal/linux/eal/eal_interrupts.c
> b/lib/librte_eal/linux/eal/eal_interrupts.c
> index 1955324d3045..b6ae12a282e7 100644
> --- a/lib/librte_eal/linux/eal/eal_interrupts.c
> +++ b/lib/librte_eal/linux/eal/eal_interrupts.c
> @@ -1239,9 +1239,9 @@ rte_intr_tls_epfd(void)
>  	return RTE_PER_LCORE(_epfd);
>  }
> 
> -int
> -rte_epoll_wait(int epfd, struct rte_epoll_event *events,
> -	       int maxevents, int timeout)
> +static int
> +eal_epoll_wait(int epfd, struct rte_epoll_event *events,
> +	       int maxevents, int timeout, bool interruptible)
>  {
>  	struct epoll_event evs[maxevents];
>  	int rc;
> @@ -1255,29 +1255,40 @@ rte_epoll_wait(int epfd, struct rte_epoll_event
> *events,
>  	if (epfd == RTE_EPOLL_PER_THREAD)
>  		epfd = rte_intr_tls_epfd();
> 
> -	while (1) {
> -		rc = epoll_wait(epfd, evs, maxevents, timeout);
> -		if (likely(rc > 0)) {
> -			/* epoll_wait has at least one fd ready to read */
> -			rc = eal_epoll_process_event(evs, rc, events);
> -			break;
> -		} else if (rc < 0) {
> -			if (errno == EINTR)
> -				continue;
> +retry:
I guess it is a personal choice. I personally prefer using goto for error handling.

> +	rc = epoll_wait(epfd, evs, maxevents, timeout);
> +	if (likely(rc > 0)) {
> +		/* epoll_wait has at least one fd ready to read */
> +		rc = eal_epoll_process_event(evs, rc, events);
> +	} else if (rc < 0) {
> +		if (errno == EINTR) {
> +			if (!interruptible)
> +				goto retry;
> +		} else {
>  			/* epoll_wait fail */
> -			RTE_LOG(ERR, EAL, "epoll_wait returns with
> fail %s\n",
> +			RTE_LOG(ERR, EAL,
> +				"epoll_wait returns with fail %s\n",
>  				strerror(errno));
> -			rc = -1;
> -			break;
> -		} else {
> -			/* rc == 0, epoll_wait timed out */
> -			break;
>  		}
>  	}
> 
>  	return rc;
>  }
> 
> +int
> +rte_epoll_wait(int epfd, struct rte_epoll_event *events,
> +	       int maxevents, int timeout)
> +{
> +	return eal_epoll_wait(epfd, events, maxevents, timeout, false); }
> +
> +int
> +rte_epoll_wait_interruptible(int epfd, struct rte_epoll_event *events,
> +			     int maxevents, int timeout)
> +{
> +	return eal_epoll_wait(epfd, events, maxevents, timeout, true); }
> +
>  static inline void
>  eal_epoll_data_safe_free(struct rte_epoll_event *ev)  { diff --git
> a/lib/librte_eal/rte_eal_version.map b/lib/librte_eal/rte_eal_version.map
> index 234487787994..e1aeb99ba9c8 100644
> --- a/lib/librte_eal/rte_eal_version.map
> +++ b/lib/librte_eal/rte_eal_version.map
> @@ -331,6 +331,7 @@ EXPERIMENTAL {
>  	rte_dev_hotplug_handle_enable;
>  	rte_dev_iterator_init;
>  	rte_dev_iterator_next;
> +	rte_epoll_wait_interruptible;
>  	rte_extmem_attach;
>  	rte_extmem_detach;
>  	rte_extmem_register;
> --
> 2.20.1