netdev - Re: [PATCH v2] fs/epoll: Enable non-blocking busypoll when epoll timeout is 0

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Date:   Mon, 6 Jul 2020 12:50:16 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     linux-fsdevel@...r.kernel.org, netdev@...r.kernel.org,
        eric.dumazet@...il.com, davem@...emloft.net,
        viro@...iv.linux.org.uk
Subject: Re: [PATCH v2] fs/epoll: Enable non-blocking busypoll when epoll
 timeout is 0

Resending.

Dave, Eric,

Can we get this in via net-next as this is targeted for networking use 
case using epoll/busypoll.

Thanks
Sridhar

On 6/24/2020 12:30 PM, Sridhar Samudrala wrote:
> This patch triggers non-blocking busy poll when busy_poll is enabled,
> 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@...el.com>
> 
> v2:
> Added net_busy_loop_on() check (Eric)
> 
> ---
>   fs/eventpoll.c | 13 +++++++++++++
>   1 file changed, 13 insertions(+)
> 
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index 12eebcdea9c8..c33cc98d3848 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.
> +		 */
> +		if (!eavail && net_busy_loop_on()) {
> +			ep_busy_loop(ep, timed_out);
> +			write_lock_irq(&ep->lock);
> +			eavail = ep_events_available(ep);
> +			write_unlock_irq(&ep->lock);
> +		}
> +
>   		goto send_events;
>   	}
>   
>