Re: [PATCH] fs/epoll: Enable non-blocking busypoll with epoll timeout of 0

["Samudrala, Sridhar" <sridhar.samudrala@intel.com>]

Adding Dave, Eric for review and see if we can get this in via net-next
as this is mainly useful for networking workloads doing busypoll.

Thanks
Sridhar

On 6/19/2020 11:13 AM, Sridhar Samudrala wrote:
> This patch triggers non-blocking busy poll when busy_poll is enabled and
> epoll is called with a timeout of 0 and is associated with a napi_id.
> This enables an app thread to go through napi poll routine once by calling
> epoll with a 0 timeout.
> 
> poll/select with a 0 timeout behave in a similar manner.
> 
> Signed-off-by: Sridhar Samudrala <sridhar.samudrala@intel.com>
> ---
>   fs/eventpoll.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 12eebcdea9c8..5f55078d6381 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1847,6 +1847,19 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
>   		eavail = ep_events_available(ep);
>   		write_unlock_irq(&ep->lock);
>   
> +		/*
> +		 * Trigger non-blocking busy poll if timeout is 0 and there are
> +		 * no events available. Passing timed_out(1) to ep_busy_loop
> +		 * will make sure that busy polling is triggered only once and
> +		 * only if sysctl.net.core.busy_poll is set to non-zero value.
> +		 */
> +		if (!eavail) {
> +			ep_busy_loop(ep, timed_out);
> +			write_lock_irq(&ep->lock);
> +			eavail = ep_events_available(ep);
> +			write_unlock_irq(&ep->lock);
> +		}
> +
>   		goto send_events;
>   	}
>   
>